Supplementary Material Available: Tables of structure factor amplitudes for the structural analyses of compounds 4 and 5 and tables of thermal parameters and hydrogen atom coordinates for each structure (34 pages). Ordering information is given on any current masthead page.

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strate, and therefore the organic halide and/or aldehyde can carry functional groups, such as alcohol, that would have to be protected in the presence of the acid chloride. Allyl chlorides are converted to aldehydes without double-bond migration to the a,@-position.In the conversion of 2-iodobenzyl alcohol to the corresponding aldehyde, the acylpalladium complex ( l ) , under the reaction conditions, apparently undergoes a transmetalation reaction and reductive elimination of the acylpalladium hydride much faster than direct reductive elimination to the lactone.' A limiting side 0 1 reaction in the conversion of halides to aldehydes appears to be the direct reduction of the halide without carbon monoxide insertion. This reduction proceeds only very slowly under the standard reaction conditions in the absence of a palladium catalyst. The slow addition of tributyltin hydride to the reaction mixture under carbon monoxide is necessary in order to optimize the ratio of aldehyde to reduced product, and the reduction also can be suppressed somewhat by increasing the carbon monoxide pressure. For example, the conversion of 4-bromoiodobenzene to 4bromobenzaldehyde by the slow addition of 1 equiv of tributyltin hydride gives a 73% yield under 1 atm CO and an 88% yield under 3 atm. The reduction pathway becomes more serious with an aryl halide that is a good electron acceptor (one-electron transfer) and/or carries +a substituents. The yields of 44trobenzaldehyde and nitrobenzene from 4-nitroiodobenzene are 9% and 84%, respectively, under 1 atm of carbon monoxide but 38% and 62% under 3 atm.Typically, reactions were run under a balloon of carbon monoxide or in a pressure bottle (3 atm) with 1-5 mmol of the organic halide in 2-5 mL of T H F or toluene per mmol of halide and 3.5-4 mol % of tetrakis(triphenylphosphine)palladium(O). A 10-mL solution of an equimolar amount of tributyltin hydride (plus a 10% excess) in the appropriate solvent was added via syringe pump over a 2.5-4-h period while maintaining the reaction mixture at 50 OC. After the addition was completed, the tributyltin halide was removed by conversion to the insoluble tributyltin fluoride.6 The aldehydes were purified by radial or flash column chromatography. Acknowledgment.We have recently reported reactions between neopentylidyne complexes and water to give oxo neopentylidene complexes of the type W(O)(CHCMe3)(PR3),C1,.' We became interested in the possibility of analogous reactions in the absence of potentially problematical phosphine ligands and therefore began exploring (1) Rocklage, S. M.: Schmck. R. R.: Churchill. h Organometallics 198the hydrolysis of simple tungsten(V1) neopentylidyne complexes. We report here two examples of hydrolysis to give oxo neopentyl complexes that are stable to -180 OC in air and to further hydrolysis.When a large excess of water is added to a concentrated solution of W(CCMe3)(CH2CMe3)32 in tetrahydrofuran white crystals form in -30 min and can be isolated in -90% yield. Analytical, NMR, and mass spectral data3 suggest that thi...

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