Rhodium complexes with secondary phosphine and phosphinite ligands and the crystal structures of...

~ Pergamon l)oh'hcdro#s Vol. 17. Nos 13 14, pp. 2345 2351, 1998

I 1998 Elsevier Sciencc Lid All righls reserved. Printed in Great Britain

P I I : 80277-5387(97)00460-9 0277 538798 $1tl.00+0.00

Rhodium complexes with secondary phosphine and phosphinite ligands and the crystal structures of [(PPh2OH)z(PPh20)Rh (g-Cl)3Rh(PPh2OH) (PPh20)2] and [ (P Ph20 H) (P Ph2 O) Cl (N CMe ) Rh

(#-CI)2Rh(PPhzOH) (PPh20)CI(NCMe)]" 2thf

Bhavesh Patel, Simon J. A. Pope and Gillian Reid*

Department of Chemistry, University of Southampton, Highfield, Southampton SO17 1 B J, U.K.

(Received 30 September 1997: accepted 11 November 1997)

Abstract --RhC13- 3H:O reacts with ca six molar equivalents of PPh2H or PCy2H in EtOH solution under a Ne atmosphere and in the presence of excess NH4PF<, to yield [RhCI:(PPh,H)4]PF~ or [RhCIqPCyzH)4}PF<> respectively as yellow solids. 3'p{~H } NMR spectroscopy shows the presence of the trans isomer only in chloro- carbon solutions, with Jm, i, ca 80 Hz. Upon standing a solution of trans-[RhCl2(PPh2H)4]PF~ in a MeCN/thf mixture results in the production of yellow crystals of [(PPh2OH)(PPhaO)CI(NCMe)RhOt-C1)eRh(PPheOH) (PPh20)CI(NCMe)]'2thf, the structure of which shows an edge-bridged bioctahedral arrangement with d(Rh. •. Rh) = 3.74 ~. The NCMe ligands lie tram to the terminal C1 ligands, while the PPh2OH and PPh20 ligands are trans to the bridging CI ligands. The crystal structure of the triply-bridged dimer [(PPh2OH)z(PPh20)Rh(I~-C1)3Rh(PPheOH)(PPh,O)2 ] has also been determined, showing a face-sharing bioctahedral arrangement, with d(Rh. -. Rh) = 3.39 A. Both dinuclear species show significant P - - O - - H .. • O - - P hydrogen-bonding interactions. {i' 1998 Elsevier Science Ltd. All rights reserved

Keywor&': rhodium: phosphine: X-ray structure; phosphinite.

In contrast to tertiary phosphines, the coordination chemistry of primary and secondary phosphines has been largely neglected. This is in part due to the fact that coordination to a metal ion leads to the P-bound proton becoming very acidic and hence these species are liable to deprotonate yielding phosphido derivatives [1]. We have been investigating the chemistry of primary and secondary phosphines with the platinum group metals with a view to using these as neutral formally two-electron donors [2-5]. In our recent work we have isolated the stable cationic species [MCI(PCy2H)3] ~ (M = P d , Pt) [2], and the neutral c o m p l e x e s [ M ' X 2 ( L ) 4 ] ( X = C1 or Br, M ' = Ru: L = PPheH, PPhH2; M' = Os: L = PPheH, PPhH_,, PCy:tt). 31p{IH} NMR spectroscopic studies, together with X-ray crystallographic studies on several

* Author to whom correspondence should be addressed.

of these, confirm the trans-dihalo arrangement, with the four neutral phosphine ligands occupying the equatorial plane. The Ru and Os compounds exhibit reversible M(l l ) / ( l l l ) redox couples [3,4]. We now report the preparation and spectroscopic characterisation of the Rh(11 ! ) species trans-[RhCle(PR,H }a] PF~, (R = Ph, Cy), together with single crystal X-ray structure determinations on two unusual chloro-bridged bioctahedral diiners [(PPhzOH)z(PPh20)RhtI~-C1)~ Rh(PPh2OH) (PPh:O):] and [(PPh2OH)(PPh.,O)CI (NCMetRh(tt-C1)~Rh(PPh_,OH)(PPhzO)CI(NCMe)] • 2thf, isolated as decomposition products.

Several Rh(l) and It(l) complexes with secondary phosphines have been reported previously, including [M(PR:H)4] ~ ( M = R h . h ; R = C y , Ph, El) and [Rh(PBu~H)3C1] [6]. Also, in an early paper Hayter reported the preparation of the neutral Rh (111 ) complexes [RhCI3(PPheH)3] and [RhCI3(PEtzH)~] by reaction of RhCI~" 3H,O with three molar equivalents of

2345

2346 B. Patel et al.

the phosphine in EtOH, although the characterisation of these species was very limited [7].

RESULTS AND DISCUSSION

Reaction of RhC13"3H20 with six molar equivalents of PPh2H or PCy2H in degassed EtOH solution affords a colour change to yellow. In the presence of NH4PF6 concentration of the solution in vacuo gives the complexes [RhClz(PPh2H)4]PF6 or [RhC12(PCyzH)4]PF6 respectively as yellow solids. IR spectroscopy confirms the presence of the phosphine ligands and v(P--H) occurs as a weak absorption at ca 2370 cm ~. In addition, strong peaks around 840 and 555 cm -z are assigned to v(PF6) and ~(PF6) respectively, confirming the presence of the non-coor- dinating anion. The electrospray mass spectra reveal peaks with the correct isotopic distributions at m/z = 883 and 847 for the former, corresponding to [RhCI(PPh2H)4] + and [Rh(PPh2H)4] +, and 965 and 767 for the latter, corresponding to [RhCI2(PCy2H)4] + and [RhCI2(PCy2H)3] +. There was no evidence for other Rh-containing species such as dimers at higher Wl/Z.

The 31p{~H} NMR spectrum of [RhC12(P- Ph/H)4]PF6 reveals a doublet at + 1.2 ppm indicative of a trans-dichloro geometry with four equivalent PPh2H ligands coordinated in the equatorial plane, JRhP = 83 HZ ; typical of Rh(III) phosphine couplings. A septet at -146.3 ppm is also observed due to the PF ;- and these signals integrate as 4 : 1. Similarly, for [RhC12(PCy2H)4]PF6 a doublet at - 5.0 ppm and septet at -146.3 ppm are observed, JRhP = 74 Hz. In both cases the proton coupled 3.p NMR spectrum shows a distinctive second order pattern due to the coordinated secondary phosphines (Fig. 1), as expected given the direct one-bond P - - H coupling, coupling to the P - - H protons from cis and trans phosphine ligands and coupling to the phenyl or cyclohexyl ring protons. These data, together with IH NMR spectroscopy and microanalyses, confirm the products to

- 5 . 0

! ' , ! !

ppm

Fig. 1. 31p NMR spectrum of trans-[RhC12(PCyzH)4]PF6 showing the coordinated phosphine region.

be the Rh(III) tetrakis-phosphine complexes trans- [RhCIz(PPh2H)4]PF6 and trans-[RhC12(PCy2H)4]PF6.

In an attempt to grow crystals suitable for a single crystal X-ray structure analysis, a solution of trans-

[RhC12(PPh2H)a]PF6 in MeCN/thf was allowed to stand for several days at ca - 1 5°C. This resulted in the formation of a few yellow columnar crystals, along with phosphine oxide. A structure analysis performed on one of these crystals showed them in fact to be the unusual (/l-C1)2 edge-bridged bioctahedral species [ ( P P h 2 O H ) ( P P h 2 0 ) C I ( N C M e) R h ( # - C I ) 2 R h (PPh2OH)(PPh20)CI(NCMe)]'2thf, formed by oxidation of the secondary phosphine complex. The structure shows (Fig. 2, Table 1) a centrosymmetric dinuclear species in which each Rh(III) centre is coordinated to two bridging C1 ligands, one terminal CI ligand, one PPh2OH, one PPh20- and one NCMe ligand, giving a distorted octahedral arrangement, Rh--P(1) = 2.267(3), Rh--P(2) = 2.268(3), Rh--CI(1) = 2.321(3), Rh--CI(2) = 2.493(2), Rh--N(1) -= 2.015(8) fi. The bridging Cls are trans to the diphenylphosphinous acid and diphenyl- phosphinite ligands, leaving the terminal C1 and NCMe ligands mutually trans. The phosphinous acid proton was located in the difference map, and the position of this between the two O atoms, together with the O(1) . . .O(2) distance of 2.38 fi, suggests a significant H-bonding interaction involving the P - - O - - H . • • O - - P fragments. This type of H-bonding arrangement has been observed previously in several species including for example [(PPh2OMe)2(PPh2OH) Ru(#-C1)3Ru(PPh2OH)2(PPh20)] [8], [PtH(PPh20"Bu) (PPhaOH)(PPh20)] [91, [Pd(S2PMe2)(PPh20)(PPh2 OH)] [10 ] and [(PPh2OH)(PPh:O)C1Rh(#-CI)3 RhCI(PPh20)(PPh2OH)] [11]. The R h . . . Rh distance is 3.74 fi in our product, indicating non-inter- acting metal centres. This compares with an Rh. . • Rh distance of 3.745(15) fit for [(Rh2 (PBu~)4C16] [12].

Since only a few crystals of this material were produced, a full spectroscopic study was not possible. Importantly however, an electrospray mass spectrum of these did not reveal the same peaks as observed for [RhC12(PPh2H)4]PF6 (above), showing instead peaks with the correct isotopic distributions at m/z = 1122 and 582, assigned to [Rh2C13(PPh2OH)2(PPh20)2] + and [RhCI(PPh2OH)(PPh20)(MeCN)] + respectively.

In a separate experiment, upon standing an ethanol solution containing RhCl3" 3H20 and three molar equivalents of PPh2H, a few orange prism crystals of a second dinuclear species, [(PPhzOH)2(PPhzO)Rh(/I- C13)Rh(PPh2OH)(PPh20)2], were produced (together with phosphine oxide and other decomposition products). The crystal structure of this material shows (Fig. 3, Table 2) a (p-C1)3 confacial bioctahedral geometry, in which one Rh(III) centre is formally ligated to two PPhgOH and one PPh20- ligands and three bridging Cl's, while the other formally has one PPh2OH, two PPh20 and three bridging Cls. The phosphinous acid protons were not identified in the difference map in this case, however they are again implicated by the

Rhodium complexes with secondary phosphine and phosphinite ligands

C ( 5 ) ~ C{31

C{2)

0(1)

O(2"l~}'- X ~" />..~_~ __..X..~'~..~ u{,) ,~) H(28)

2347

O(lq ~ ' ~ ) v t , ~ ) C1(2")

0(2)

C{20)

~') C(21)

Fig. 2. View of the structure of [(PPh2OH){PPh20)CI(NCMe)Rh(I~-CI)2Rh(PPh2OH)(PPh20)CI(NCMe)] with the numbering scheme adopted. Atoms marked * are related by a crystallographic inversion centre.

Table I. Selected bond lengths and angles for [(PPh2OH)(PPh20)CI(NCMe)Rh(IL-CI)2Rh(PPh2OH)(PPh:O)CI(NCMe)]

Bond lengths (A) Atom Atom Distance Atom Atom Distance

Rh( 1 ) CI( 1 ) 2.321 {3) Rh( 1 ) C1(2)* 2.493 (2) Rh (1) C1(2) 2.500(3) Rh( 1 ) P(l) 2.267(3) Rh( 1 ) P(2) 2.268(3) Rh( 1 ) N (1) 2.015(8) P( I ) O(1) 1.552(6) P( 1 ) C( 1 ) 1.823(10) P{ 1) C(7) 1.808(9) P(2) 0(2) 1.549(6) P(2) C(13) 1.801(10) P{2) C(19) 1.803(9) N(I) C(25) 1.14(1) C(25) C(261 1.461 I)

Bond angles ( ) Atom Atom Atom Angle Atom Atom Atom Angle CI(I) Rh(l) C1(2) 93.23(9) CI(I} Rh(1) C1(2) 96.35(9) CI(I) Rh(l) P(l) 86.37(10) CI{I) Rh(1) P(2) 89.40(9) CI(1) Rh(1) N(I) 176.9(2) C1(2) Rh(1) C1(2)* 83.04(8) C1(2) Rh(1) P(1) 94.35(9) C1(2) Rh(I) P(2) 171.90(10) C1(2) Rh(1) N(1) 83.7(2) C1(2)* Rh(l) P(I) 176.3(1) C1(2)* Rh(1) P(2) 89.06(9) C1(2)* Rh(1) N(1) 83.7(2) P(I) Rh(1) P(2) 93.5(1) P(I) Rh(l) N(I) 93.5(2) P{2) Rh(l) N(I) 93.7(2) Rh(l) C1(2) Rh(l)* 96.96(8) Rh(l) P(I) O(1) 114.4(3) Rh(1) P(I) C(1) 116.0(3) Rh(I ) P(I) C(7) 109.1 (3) O(1 ) P(1) C( I ) 104.5(4) O(1) P(1) C(7) 107.7(4) C{1) P(1) C(7) 104.5(4) Rh(I) P(2) 0(2) 115.3(3) Rh(I) P(2) C(13) 107.7(3) Rh(1) P(2) C(19) 118.3(3) 0(2) P(2) C(13) 107.5(4) 0(2) P(2) C(19) 103.4(4) C(13) P(2) C(19) 103.6(4)


P(2*) C1(2) P(3)

0(2*) ~ 0(3)

O( 0(2)

o(1)

P(I*) CI(1) P(1)

Fig. 3. View of the structure of [(PPh2OH)2(PPh20)Rh(~-CI)3Rh(PPh2OH)(PPh20)2] (a) with the numbering scheme adopted and (b) showing the chloro-bridged core. Atoms marked * are related by a crystallographic 2-fold axis.

O. ." O distances, O(1) ' . . 0(2) = 2.55, O(1) . . .O(3) = 2.54, 0 ( 2 ) . . . 0 ( 3 ) = 3.01 A. Hence these interatomic distances suggest that the most plausible arrangement is for O(1) to be deprotonated, since this allows a significant H-bonding interaction of O(1) with both the proton on 0(2) and 0(3). The third phosphinous acid proton is disordered across a crystallographic two-fold axis and must be associated with either 0(2) or 0(3) and only on one half of the molecule. However, there is little doubt over its presence since otherwise, counting charges would imply a Rh(II)/Rh(III) dimer which is highly unlikely, and further, there was no evidence for any other species in the difference map. Stephenson and co-workers reported a similar disorder problem in the structure of the Ru(lI)/Ru(lI) dimer [(PPh2OEt)2(PPh2OH)Ru(/~-

CI)3Ru(PPh2OH)2(PPh20)], which also crystallises in the space group Faaa with a half-molecule in the asymmetric unit. In this case there was substantial disorder of the PPh20- and PPh2OEt ligands about a two-fold axis or centre of symmetry [8]. They also reported a full structure determination on the related confacial bioctahedral Ru(II)/Ru(II) dimer [(PPh2 OMe)2(PPh2OH)Ru(~-CI)3Ru(PPh2OH)2(PPh20)], formed by pyrolysis of [PPh2OMe)3Ru(/~-CI)_~Ru(P-

Ph2OMe)3]C1 for 12 h at 120°C [8]. The R h . ' . R h distance in [(PPh2OH)2 (PPh20) Rh (#-C1)3Rh (PPh2OH)(PPh20)2] is 3.39 A. The only previously reported dinuclear Rh(lll) complex which involves similar phosphinito ligation is the anionic dimer [(PPh2OH) (PPh20) C1Rh(#-CI)3RhCI(PPh20) (PPh2

OH)]- for which d(Rh. . . Rh) is 3.2262(16) [11].

Rhodium complexes with secondary phosphine and phosphinite ligands 2349

Table 2. Selected bond lengths and angles for [(PPh2OH)2(PPh20)Rh(#-C1)~Rh(PPh2OH)(PPh20)2]

Bond lengths (A) Atom Atom Distance Atom Atom Distance

Rh(l/ CI(1) 2.517(5) Rh(l) CI(1)* 2,458(5) Rh(I) C1(2) 2.459(5) Rh(l) P(1) 2,293(6) Rh(l) P(2) 2.312(6) Rh(1) P(3) 2.282(5) P(I) Oil) 1.55(1) P(I) C(I) 1.81(2) P(ll C(7) 1.85(2) P(2) 0(2) 1.59(2) P(2) C(13) 1.82(2) P(2) C(19) 1.83(2) P(3) 0(3) 1.56(1) P(3) C(25) 1.79(2) P(3) C(31) 1.84(2)

Bond angles () Atom Atom Atom Angle Atom Atom Atom Angle Cl(I) Rh(1) Cl(l)* 78.4(2) Cl(1) Rh(1) C1(2) 77.811) Cl(l) Rh(l) P(1) 96.8(2) CI(1) Rh(1) P(2) 99.2(2) Cl(I) Rh(1) P(3) 171.5(2) CI(1) Rh(1) C1(2) 78.9(I) CI(I)* Rh(1) P(1) 99.9(2) CI(1)* Rh(l) P(2) 171/.9(2i CI(I)* Rh(l) P(3) 93.5(2) C1(2) Rh(1) P(I) 174.6(2) C1(2) Rh(1) P(2) 92.0(2) C1(2) Rh(1) P(3) 98.1(21 P(I) Rh(I) P(2) 89.1(2) P(I) Rh(l) P(3) 87.2(2) P(2) Rh(l) P(3) 88.4(2) Rh(1) CI(I) Rh(l)* 85.9(2) Rh(I) (71(2) Rh(l)* 87.1(2) Rh(1) P(l) O(1) 113.5(6) Rh(1) P(I) C(1) 116.9(7) Rh(1) P(l) C(7i 112.9(7) O(1) P(1) C(I) 103.4(9) O(1) P(1) C(7) 106.9(9) C(I) P(1) C(7) 102.1(9) Rh(1) P(2) 0(2) 113.7(6) Rh/I) P(2) C(13) 114.0(7) Rh(1) P(2) C(19) 114.8(7) 0(2) P(2) C(13) 102.8(9) 0(2) P(2) C(19) 105.8(9) Ctl3) P(2) C(19) 104.5(9) Rh(I) P(3) 0(3) 112.3(5) Rh(I) P(3) C(25) 115.0(7) Rh(1) P(3) C(31) 114.1(61 O(31 P(3) C(25) 105.6(8) 0(3) P(3) CI31) 1(16.7(8) (;(25) P(3) C(31) 102.1(9)

A mass spectrum of the remaining crystals showed peaks around m/z = 1487 corresponding to loss of one CI from the neutral dimer, and once again there was no evidence for any rhodium species involving PPh2H ligands. Furthermore, an IR spectrum showed peaks due to the PPh2OH and PPh20 ligands as well as a weak absorption at 253 cm -1 assigned to v(Rh--Clbridging).

These results show that while PPh2H and PCy2H react readily with Rh(lI1) to give the tetrakis phosphine cations [RhC12(L)4] +, the diphenylphosphine complex is not very stable in solution, readily under- going oxidation and dimerisation. This is in contrast to the behaviour of the Ru(II) and Os(lI) species trans-[MX2(L)4] (X = CI or Br; L = PPh2H, PCy2H, PPhH2) which are apparently much more stable [3,4]. The dinuclear species reported here presumably precipitate out of solution due to their poor solubilities. Prior to this work there was only one reported Rh(II1) chloro-bridged dimer involving phosphinite ligands [11]. Current work is aimed at finding alternative. more direct, synthetic routes to these and other rhodium phosphinite derivatives.

EXPERIMENTAL

Infrared spectra were measured as KBr or Csl discs or as Nujol mulls using a Perkin-Elmer 983G spectrometer over the range 1804000 cm ~. Mass spectra were run by positive electrospray (ES) using a VG Biotech Platform. ~H NMR spectra were recorded using a Bruker AM300 spectrometer operating at 300 MHz. 3LP{~H} NMR spectra were recorded in 10 mm o.d. tubes containing ca 10% deuterated solvent, using a Bruker AM360 spectrometer operating at 145.8 MHz and are referenced to external 85% H3PO4 [~5(31P) = 0]. Microanalyses were performed by the Imperial College microanalytical service. PCy,H was purchased from Strem and PPh2H was prepared by the literature procedure [13].

PREPARATIONS

trans-[RhC12(PPh2H)4]PF6

RhCI3"3H20 (0.106 g, 0.40 mmol), PPh2H (0.45 ml, 2.4 mmol) and a small excess of NH4PF~ (0.08 g,


0.5 mmol) were added to stirring, degassed E tOH (30 cm 3) under a N2 atmosphere. This solution was stirred at room temperature for 1 day during which time a light yellow precipitate was deposited. This was collected by filtration, washed with Et20 and dried in vacuo (Yield : 0.41 g, 95%). Calc. for C48H44C12F6PsRh : C = 54.2, H = 4.1% ; Found : C = 53.8, H = 3.8%. Electrospray mass spectrum (MeCN) : found m/z = 883, 847; Calc. for ['°3Rh35Cl(PPh2H)4] + m / z = 882, ['°3Rh(PPh2U)4] + m/z = 847. 3tp{ iH} N M R spectrum (CHeCI2/CDCI 3, 300 K) : 6 + 1.2 (d, PPh2H, 4P, JRhP = 83 HZ), -- 146.3 (spt, P F 6 , 1P). ~H N M R spectrum (300 MHz, CDC13, 300 K) : 6 7.1-7.4 (m, Ph), 5.7 (m, PH). IR spectrum (CsI disk) : 3051 w, 2372 w, 1460 m, 1375 m, 1308 m, 1182 m, 1161 m, 1071 m, 923 m, 840 vs, 735 m, 557 s, 504 m, 477 w, 448 m, 420 w, 365 w c m - ~.

trans-[RhCl2(PCy2H)4]PF6

RhCI3"3H20 (100 mg, 0.38 mmol) dissolved in a minimum volume of H20 was added to deoxygenated E tOH (20 cm3). Excess PCy2H (0.45 cm 3, 2.3 mmol) was added to the solution and the mixture was refluxed under N2 for 3 h, yielding a yellow solution. Addit ion of excess NH4PF6 gave a yellow solid which was collected by filtration, washed with Et20 and dried in vacuo (Yield : 0.22 g, 52%). Calc. for C48HssCI2F6PsRh: C = 51.9, H = 8 .3%; Found : C = 5 1 . 6 , H = 8 . 1 % . Electrospray mass spectrum (MeCN) : found m/z = 965, 767; calculated for ['°3Rh35C12(PCy2H)4] + m/z = 965, ['°3Rh35C12(P- Cy2H)3] + m/z = 767. 3~p{~H} N M R spectrum (CH2CI~/CDCI3, 300 K) : 6 - 5 . 0 (d, PCy2H, 4P, JRhP = 74 HZ), -- 146.3 (spt, P F 6 , 1P). IR spectrum (CsI disk) : 2921 s, 2851 sm, 2362 w, 2321 w, 1460 m, 1375 m, 1290 w, 1263 w, 1226 w, 1199 w, 1175 w, 1075 m, 1048 w, 1002 m, 936 w, 920 w, 836 vs, 722 m, 559 s 513 wm 478 m, 449 w, 432 w, 389 w, 343 m, 281 w cm-].

X-RAY CRYSTALLOGRAPHY

[ ( P P h 2 O H ) ( P P h 2 0 ) C I ( N C M e ) Rh(/~-C1)2 Rh(PPh2 OH) (PPh20)CI(NCMe)] • 2thf

Yellow, columnar crystals of [(PPh:OH)(PPh20) C I ( N C M e ) R h ( # - C I ) 2 R h ( P P h 2 O H ) ( P P h 2 0 ) C I (NCMe)] • 2thfwere obtained from a solution of trans- [RhC12(PPh2H)4]PF6 in MeCN/thf . The selected crystal (0.30 x 0.20 x 0.15 mm) was coated with mineral oil and mounted on a glass fibre under a cold stream of N2 gas.

Crystal data. C60H56C14N_,O6P4Rh> M---1372.6, triclinic, space group P~ (#2) , a = 13.056(2), b = 13.920(3), c = 9.276(4) A, c~ = 107.50(2), JJ = 100.50(2), 7 = 103.32(2) °, V = 1504.4(8) •3 [from 20 values of 20 reflections measured at + m],

2 = 0.71073 A, Z = 1, D,.,I, = 1.515 g cm -3,/~ = 8.82 cm -~, F(000) = 696.

Data collection and processing. Data collection used a Rigaku AFC7S diffractometer equipped with an Oxford Systems cryostream operating at 150 K, using graphite monochromated Mo-K~ radiation, (09-20 scan technique), 5542 data collected (20max 50.0"), 5290 unique data (Ri,,, = 0.063 based on F2). As there were no identifiable faces an empirical absorption correction was applied using 0-scans (min. and max. transmission factors were 0.738 and 1.000 respectively).

Structure solution and refinement. The structure was solved by direct methods [14] and expanded using Fourier techniques to locate all non-H atoms in the half-molecule in the asymmetric unit (related to the other half by a centre of symmetry) [15]. During refinement one fully occupied T H F solvent molecule was also identified in the asymmetric unit. All non- H atoms were refined anisotropically and hydrogen atoms were included in fixed calculated positions [with d ( C - - H ) = 0.96 A] but not refined. The H atom associated with the PPh2OH ligands was located in the difference map and included but not refined. The final cycle of full-matrix least-squares refinement (on F) was based on 2859 observed reflections with (I > 2.5a(I)) and 352 variable parameters and converged with R = 0.053, R,. 0.059, using the weighting scheme w--~ = a2(F). The maximum residual peak and minimum residual trough corresponded to + 1.33 and - 1 . 4 5 eA 3. Selected bond lengths and angles are given in Table 1.

[(PPh2OH)2(PPh20)Rh(I~-CI)3Rh(PPh2OH) (PPh20)2]

Orange prisms of [(PPh2OH)2(PPh20)Rh(#- C1)3Rh(PPh2OH)(PPh20)2] were obtained from a solution of RhCI3" 3H20 (0.094 g, 0.36 mmol) and three molar equivalents of PPhzH (1.08 mmol) in E tOH (20 cm3), which was refluxed for one hour to give an organge solution, and then maintained at ca - 1 5 ° C over several days. The selected crystal (0.55 x 0.40 x 0.30 mm) was coated with mineral oil and mounted on a glass fibre under a cold stream of

N2 gas. Crystal data. C72H63CI306P6Rh2, M = 1522.30,

orthorhombic, space group Fddd, a=25 .861(6 ) , b = 43.002(5), c = 23.924(5) A, v = 26605(7) A 3 [from 20 values of 20 reflections measured at __+o], 2 = 0.71073 ~ , Z = 16, D,,/,. = 1.520 g cm -3,/2 = 8.13 cm ~, F(000) = 12384.

Data collection and processin#. Data collection used a Rigaku AFC7S diffractometer equipped with an Oxford Systems cryostream operating at 150 K, using graphite monochromated Mo-K~ radiation. Using the 09 scan technique 6235 data were collected (20ma x 50.0°). AS there were no identifiable faces an empirical absorption correction was applied using g,-scans (min.

Rhodium complexes with secondary phosphine and phosphinite ligands

and max. transmission factors were 0.910 and 1.000 respectively).

Structure solution and refinement. The structure was solved by direct methods [14] and expanded using Fourier techniques to locate all non-H atoms in the half-molecule in the asymmetric unit (related to the other half by a crystallographic two-fold axis) [15]. The Rh, CI, P and O atoms were refined anisotropically and hydrogen atoms were included in fixed calculated positions [with d (C- -H) = 0.96 A.] but not refined. The H atoms associated with the PPh2OH ligands were not located in the difference map, and were therefore omitted from the final structure factor calculation. The final cycle of full-matrix least-squares refinement (on F) was based on 2461 observed reflections with (I > 2.5cr(/)) and 222 variable parameters and converged with R = 0.076, R, 0.104, using the weighting scheme w ~ = a2(F). The maximum residual peak and minimum residual trough corresponded to + 2.19 (attempts were made to refine this as a partially occupied O atom e,g. from a H20 solvent molecule, but without success) and -0 .78 e A 3. Selected bond lengths and angles are given in Table 2.

Atomic coordinates, anisotropic thermal parameters and bond lengths and angles for the two structures have been deposited at the Cambridge Crystallographic Data Centre (CCDC).

Acknowled, qements -We thank the EPSRC for a studentship (S.J.A.P.) and flgr provision of the X-ray diffractorneter. We also thank Johnson Matthey plc for loans of RhCL" 3H,O.

REFERENCES

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