Molybdenum complexes formyls

The oxomolybdenuni(IV) porphyrin treated with trimethylsilylchloride produces the trans dichloro derivative Mo(OEP)Cl2 which gives Mo(OEP)(PhC=CPh) by reduction with LiAlH4 in the presence of diphenylacetylene. The dimer is then obtained by vacuum pyrolysis of this five coordinate complex. Molybdenum(II) dimers are also obtained by heating a mixture of MoCl2(CO)4 and H2(Por) in oxygen-free toluene (Eq. 26) where Por is OEP, its 5-formyl-, 5-amino-, and 5-isocyanato derivative, or 5,15-dimethyletiopor-phyrin II. 

A hydride is one of the simplest nucleophiles, and Casey ° and Gladysz have prepared kinetically stable formyl complexes by the direct attack of hydride on a number of neutral chromium-, molybdenum-, and iron-carbonyl complexes (Equation 11.2). Although these complexes are relatively electron rich, because they possess zero-valent metal centers, the negative charge in the product can be stabilized by the remaining -ir-ac-cepting CO ligands. 

The synthesis and further transformation of formyl complexes via hydrido-acyl intermediates into ti2-acetaldehyde complexes has been reported.S7 The molybdenum(II) carbonyl complex, [Mo(CO)3Me(Ti5-Cp)l, was found to react with Li[BHEt3l in THF at -66 °C to yield the formyl complex, [Mo(CHO)(CO)2Me(Ti5-Cp)]-. Slow warming allowed the spectroscopic observation of successive rearrangements of the formyl complex into hydrido-acyl and, finally, ti2-acetaldehyde derivatives. Scheme 10.9. 

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