Supplementary Material Available: Detailed results of the X-ray crystal structure of (r/-C5Me5)2Os2(CO)2(Ai-H)2, tables of experimental details, positional and thermal parameters, general temperature factor expressions (U,B), bond distances, and bond angles, and the structure of (7/-C5Me5)2Os2(CO)2^-H)2 (8 pages). Ordering information is given on any current masthead page.

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The inherent sensitivity and simplicity make the new experiment generally applicable to a number of biological and chemical systems where observation of 15N chemical shifts has proven time consuming or impossible because of the low natural abundance and NMR sensitivity of 15N. Pulse sequences with more than one pulse applied to the observed nuclei5 make suppression of unwanted signals harder and do, in practice, not provide the improvement that might be expected.16Acknowledgment. The sample of gramacidin S was kindly provided by Professor D. H. Live (Rockefeller University). We are indebted to professor Gary Maciel for many valuable comments in preparing the manuscript and further gratefully acknowledge use of the Colorado State University Regional NMR Center, supported by National Science Foundation Grant CHE-8208821. A.B. acknowledges support from the Department of Energy (Laramie Energy Technology Center), and R.H.G. was supported by NSF Grant PCM 79-16861, awarded to C. D.Poulter.

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evidence, including *H labelling, is presented to show that photolysis of [(q5-C5R5)M(C0),] complexes (M = Rh, R = Me; M = Ir, R = H, Me) in CH4 matrices at 12 K leads primarily to [(q5-C,R5)M(CO)(H)(Me)] species whereas in Ar and N2 matrices only small yields of {(q5-C5R5)M(CO)] species are observed. One of the most important goals in the petrochemicals [(q5-C5R5)M(CO)2] [(r5-CsMes>Ir(Co)(H)(Me)l (4) industry is to find catalysts which will activate saturated hydrocarbons, particularly CH4, so as to enable their use as feedstocks.' The recent discoveries that [ ( T ~-C ~R ~) I ~( C O ) ~] complexes [R = H (l), Me (2)] would photochemically activate C-H bonds in CH4,2a neopentane,zb cyclohexane72b and benzene,2b and that [ (q5-C5Me5)M(PMe3)H2] (M = Rh,3 Ir4) could similarly activate C-H bonds in alkanes have (