Multiple metal-carbon bonds. 36. Metathesis of molybdenum-molybdenum triple bonds with acetylenes to give alkylidyne complexes

Abstract

Organometallics noted when I3C-enriched W(CO),THF was added to the S [ Cr3(C0)12] 2-anion.Acknowledgment. The financial support of the Robert A. Welch Foundation is greatly appreciated. [ Na] [ PPN] [ ((CO),Cr),S], 87039-34-7; (w-CO)& C0)&r3(p4-S)Cr-(CO)52-, 87050-03-1; Cr(CO)STHF, 15038-41-2; W(CO)5THF, Registry NO. 1,91670-43-8; 2% [PPN+]p(CH&CO, 91670-45-0; 36477-75-5. Summary: Mo,(OCMe,), reacts with phenylacetylene in pentane to produce Mo(CPh)(OCMe,), in -60 % yield (by 'H NMR) in -2 h. I t can be isolated by sublimation in -30% yield. In the presence of quinuclidine (quin) Mo,(OCMe,), reacts with phenylacetylene to yield an inseparable 1 : 1 mixture of Mo(CPh)(OCMe,),(quin) and Mo(CH)(OCMe,),(quin) in a combined yield of -60 % . Analogous reactions between Mo,(OCMe,), and l-pentyne in the presence of quinuclidine yield oily 1-pentyne oligomers containing a mixture of Mo(CPr)(OCMe,),(quin) and Mo(CH)(OCMe,),(quin) in -50% yield (by 'H NMR).In the absence of quinuclidine only Mo(CPr)(OCMe,), is observed by NMR in the oily product mixture. Addition of acetylene to Mo,(OCMe,), yields what we propose to be Mo,(OCMe,),(p-C,H,), which upon attempted recrystallization loses acetylene to reform MO,(OCMe,),.Summary: Acyl chlorides can be selectively and rapidly reduced, under mild conditions, by group 66 anionic hy-(1) On leave from the

Molecular and Silica-Supported Molybdenum Alkyne Metathesis Catalysts: Influence of Electronics and Dynamics on Activity Revealed by Kinetics, Solid-State NMR, and Chemical Shift Analysis

“…7,13,[36][37][38][39][40][41][42][43] Despite these advances, alkyne metathesis catalysts would still benefit from improved activity and stability. Several deactivation mechanisms have been identified such as the bimolecular elimination of alkyne, 44 the formation of metallatetrahedrane species [45][46][47] or cyclopentadienyl species, 45 as well as, in the case of terminal alkynes, deprotonation of the intermediate metallacyclobutadienes, resulting in polymerization. 7,[14][15][16] One strategy to increase the stability of molecular catalysts is to use the surface organometallic chemistry (SOMC) approach.…”

Insights into the Metathesis Reaction Involving M−M, C−C, and M−C Triple Bonds from Computations Employing Density Functional Theory on Model Compounds M2(OH)6 and M2(SH)6, Where M = Mo and W

“…7 In work in our laboratory, we had observed the formation of alkyne adducts in a variety of reactions employing M 2 (OR) 6 compounds, where M ) Mo and W and R ) t Bu, i Pr, and CH 2 t Bu. In certain cases, we also found evidence for an equilibrium involving the alkyne adducts and the alkylidyne complexes, eq 4, but only when the metal was tungsten.…”

Efficient catalytic alkyne metathesis with a fluoroalkoxy-supported ditungsten(III) complex

“…Thus, we attempted the cleavage of the M≡M bond of Mo2F6 and W2F3 by an alkyne to generate the corresponding benzylidyne complexes. Unfortunately, as reported in the past by Schrock [ 62 , 87 ], we could not achieve the selective cleavage of the triple bond in Mo2F6 by internal or terminal alkynes to isolate the corresponding alkylidyne complex. In an NMR study on the cleavage of the Mo≡Mo triple bond, in which Mo2F6 was treated with two equivalents of 1-phenyl-1-propyne, no signals corresponding to a possible molybdenum alkylidyne complex were detected in the 1 H and 19 F NMR spectra over a period of three days.…”

“…The metal–metal triple bond of many ditungsten complexes can be cleaved by alkynes in a metathesis-like reaction to form the corresponding alkylidyne complexes [ 62 , 86 ]. Dinuclear Mo≡Mo complexes, however, have not yet been cleaved efficiently by alkynes [ 87 ].…”