Molybdenum-nitrogen triple bond formation drives cleavage

ArRN—Mo* xNRAr N2

*NRAr

ArRN / - M o ^ N R A r NRAr

+

Ν

ArRN /M o C*NRAr

ArRN' , Μο'/ζ,,κ

NRAr

Mo(NRAr)3

ArRN^ ArRN^Mo-

Ν

Ν

.NRAr

NRAr ArRN / M o ^NRAr

NRAr Mo(NRAr)3 complex shows molybdenum in purple, nitrogen in

Ar = 3,5-C6H3(CH3)2 R = C(CD3)2CH3 ^/we, an^ car\)0n {n gray.

Molybdenum complex cleaves Ν Ν bond Chemists at Massachusetts Institute of Technology have shown that a molybde­num complex they synthesized can split the very strong triple bond of molecular nitrogen to form a nitrido complex.

The unprecedented reactivity of the complex could have important practical applications in harnessing atmospheric nitrogen as a chemical feedstock. And the complex's chemistry could shed light on the mechanism of biological nitrogen fixation by nitrogenase, a process that re­mains poorly understood.

Christopher C. Cummins, an MIT as­sistant professor of chemistry, and Cata-lina E. Laplaza, an MIT undergraduate, carried out the research, which was sup­ported by the MIT chemistry depart­ment. The work with N2 follows the re­cent report from Cummins' lab that his molybdenum complex cleaves the nitro­gen-nitrogen multiple bond in N 2 0 (C&EN, May 8, page 27).

Obtaining what amounts to "a net six-electron reduction of N2 in this pre­sumed binuclear N2 adduct is just re­markable," comments Eric A. Maatta, a chemistry professor at Kansas State University, Manhattan. "I really think it's going to be a landmark transforma­tion. I'm positive it will have repercus­sions in several different areas."

Cummins' team made the Mo(NRAr)3 complex—R is C(CD3)2CH3 and Ar is 3/5-C6H3(CH3)2—with the goal of pro­ducing a species that could engage in three-electron redox processes, which are rare. It chose the bulky amido sub-stituents to prevent dimerization of the complex, a common phenomenon with molybdenum(III) complexes.

In their initial work, the MIT chem­ists carried out the purification of the red-orange complex by recrystalliza-tion from ethyl ether at -35 °C under an argon atmosphere. When they at­tempted the purification under an N2 atmosphere, the solution rapidly took on an intense purple color. The chem­ists used deuterium nuclear magnetic resonance spectroscopy to monitor the purple species, thought to be a (ArRN)3Mo-N2-Mo(NRAr)3 complex [Science, 268, 861 (1995)].

Cummins and Laplaza also exposed a toluene solution of Mo(NRAr)3 to N2, producing a purple solution in about

48 hours. When they warmed the solu­tion to 30 °C, it gradually turned gold. Proton NMR spectroscopy showed that the compound responsible for the gold color was N=Mo(NRAr)3, indicating cleavage of the N2 bond.

"We've demonstrated clearly that mo­lybdenum in a three-coordinate environ­ment can effect the reductive cleavage of N2 to give a terminal nitride," Cummins observes. Although nitrogenase, which contains molybdenum, probably doesn't work through a mechanism analogous to the nitrogen splitting reaction carried out by Mo(NRAr)3, Cummins thinks the chemistry of his complex likely will prompt new thinking about nitrogenase.

Maatta thinks the approach is likely to have industrial applications. "Using N2 as a feedstock is something people have

After weeks of debate and several failed attempts to invoke cloture on a Democratic filibuster, the Senate last week passed a bill to reform U.S. prod­uct liability laws by a vote of 61 to 37.

The bill would limit punitive damag­es in most product liability suits to twice the compensatory damages (economic losses plus noneconomic losses due to pain and suffering), or $250,000, whichev­er is greater. It would also eliminate joint liability for noneconomic losses. This means that to collect noneconomic dam­ages from several defendants, a plaintiff must prove each defendant's degree of fault. In addition, the bill cuts off most rights to sue if the product is more than 20 years old at the time of injury.

tried to do for a long time/' he says. "But there have been huge thermodynamic barriers to overcome. It's remarkable that [Cummins' reaction] goes so cleanly and rapidly at room temperature."

The discovery opens up a number of lines of inquiry, according to Cummins. "The most immediate is to scrutinize more closely the mechanism of the cleavage reaction," he says. "We also want to see if we can incorporate the ni­trido nitrogen atom into organic nitro­gen compounds or convert it into am­monia." The ΜΓΓ chemists are also look­ing for examples of N2 cleavage reactions by molybdenum complexes containing more stable ligands and by complexes containing other biologically important metals such as vanadium.

Rudy Baum

The Senate bill is similar in some ways to the product liability bill (H.R. 956) passed in the House. The House bill is much broader, however. It places a cap on punitive damages for all civil law­suits, including medical malpractice suits. It also includes the "FDA de­fense"—a prohibition on the imposition of punitive damages if the product found to cause injury was approved by the Food and Drug Administration.

During Senate debate, Majority Lead­er Bob Dole (R-Kan.) tried to broaden the scope of the bill so it would resemble more closely the House legislation. But when Dole was threatened with defeat-by-filibuster of the broader legislation, he accepted a much narrower bipartisan

Senate approves product liability reform law

MAY 15,1995 C&EN 5

NEWS OF THE WEEK

compromise. A conference committee must now resolve differences.

The Chemical Manufacturers Associa­tion is pleased with the Senate bill. "The Senate bill will inject a healthy—and much needed—dose of fairness in the system," says CMA President Fred Webber. The Pharmaceutical Research & Manufacturers Association also favors the Senate bill but wants the final legis­lation to include the "FDA defense.,,

Consumer groups, such as Citizens Allied for Safety & Accountability (CASA, a coalition that includes trial lawyers and consumer organizations) and U.S. Public Interest Research Group (PIRG) are working to kill the bill in con­ference, says Edmund M. Mierzwinski, U.S. PIRG program director. Among other things, they object to the legisla­tion's preempting strong state laws but allowing weaker ones to stand.

"The tort reform legislation passed by the Senate severely limits legitimate product liability cases which expose dangers, punish wrongdoers, and pro­vide fair compensation for injured vic­tims," says Robert Brandon of CASA.

One acrimonious debate surrounding the legislation concerns the actual cost to the U.S. economy of current liability laws. An oft-quoted figure is that each U.S. consumer spends an annual aver­age of $1,200 in higher prices to cover product liability expenses for businesses. But a 1987 Conference Board survey of risk managers at 232 large corporations found that two-thirds of the managers said product liability contributed 1% or less to final product prices. Sen. Jay D. Rockefeller (D-W.Va.), who proposed the Senate compromise along with Sen. Slade Gorton (R-Wash.), counters, "It is the threat of litigation that is the problem."

Observers expect the congressional conference committee to come up with a final bill that resembles the Senate bill. But it is unclear whether President Clin­ton will sign it. "Unfortunately, the [Sen­ate] legislation in its present form does not go far enough toward balancing the interests of consumers with those of manufacturers and sellers," White House Press Secretary Michael McCurry said in a statement.

Bette Hileman

U.S. and China promote chemical trade links A 10-day visit to the U.S. by a high-lev­el Chinese delegation led by Minister of Chemical Industry Gu Xiulian has given a boost to chemical trade ties be­tween the two nations.

Gu met with Commerce Secretary Ron­ald H. Brown and with officials from the U.S. Trade Representative's office, the Energy Department, the Chemical Manufacturers Association, and other

U.S. boosts chemical trade with China

$ Millions

Fertilizers Organic chemicals Primary plastics Inorganic chemicals Dyes, coloring materials Nonprimary plastics Pharmaceuticals Oils, perfumes &

cleansing products Other chemical

materials & products

TOTAL CHEMICAL TRADE

Source: Department of Commerce

Exports

1993

$293 204 168 25 29 22 27 21

51

$840

1994

$ 944 230 140 38 32 22 22 21

53

$1,502

Imports

1993 1994

$ 0 $ 0 127 176

16 12 134 210 39 44

6 10 126 139 35 44

92 105

$575 $740

groups. Her delegation also visited chemical firms in several states.

However, a central focus of the mis­sion was the first official meeting of a Chemicals & Allied Products Subgroup of the U.S.-China Joint Commission on Commerce & Trade (C&EN, Sept. 5, 1994, page 6). The meeting in Washing­ton, D.C., was cochaired by Michael J. Copps, the Commerce Department's dep­

uty assistant secretary for basic industries, and Chen Lihua, director general of the Department of Interna­tional Cooperation in Chi­na's Ministry of Chemical Industry. Government and chemical industry officials participated.

"We've established good working relation­ships with the Chinese, seeking together to identi­fy opportunities and over­come obstacles," Copps tells C&EN. Missions have gone to China in the areas of paint and coatings, wa­ter treatment chemicals and equipment, plastics

additives, and plastics. So far, the mis­sions have led to several joint ventures, with more under discussion. Commerce also has organized the first U.S. pavilion at a chemical industry fair in Beijing.

The two sides now plan a food pro­cessing chemicals mission to China in September and an industrial surfactants mission in November. Both missions will include technical seminars. A leath­er chemicals mission also is being planned.

The subgroup will meet again in Bei­jing next month to plan missions for 1996. It also will explore chemical train­ing programs, including holding a chemical business training seminar in China. "Training is a high area of priori­ty for the Chinese," Copps notes.

The meeting also focused on obsta­cles to U.S. trade and investment in China, including the investment cli­mate and difficulties created by restric­tive new environmental regulations. "There's been some progress, but sig­nificant problems remain," Copps says.

The issue of intellectual property protection and market access has re­cently been addressed by a U.S.-China agreement that averted a trade war (C&EN, March 6, page 9). "The whole key is enforcement," Copps notes. "We'll be watching closely. It's ex­tremely important for our companies."

Acquiring information about the Chinese chemical industry is another U.S. interest, he adds. For example, "What does privatization mean there?" He points out that China views the chemical sector as one of several top-priority "pillar industries," and is now developing a strategic plan for it that probably will be ready next year. "We view China as the fastest growing mar­ket for chemicals in the world," Copps says. "And U.S. companies can contrib­ute and compete."

Richard Seltzer

New W.R. Grace chief avows firm's future With the mood buoyed by strong stock performance, an upbeat chief executive officer Albert J. Costello told W.R. Grace shareholders at the May 10 annual meet­ing in Boca Raton, Fla., to look not at the tumultuous events of the past two months, but to the future. In the next 30 to 60 days, he plans an aggressive cost-

6 MAY 15,1995 C&EN