Formyl metal complexes

The CO reductions generally could likely proceed through formyl intermediates, probably at a multinuclear site (420) hydride migration to a coordinated CO [e.g., as in the hypothetical scheme outlined in Eq. (72)] has not yet been observed, although metal formyl complexes have been synthesized via other methods (422-425). A ir-bonded formyl also seems plausible (426), since 7r-bonded acyl groups have been demonstrated (427). A stoichiometric hydrogen reduction of CO to methanol under mild conditions via a bis(pentamethylcyclopentadienyl)zirconium complex is considered to go through a formyl intermediate (428, 429) ... 

Bimolecular decomposition of a non-metal hydride organometallic complex, such as metal formyl complexes, which may involve metal hydride precursors MC( = 0)H + H20 <-> M(CO)+ + OH + H2 N/A 36... 

Reaction (64) demonstrates the production of a metal formyl complex by intermolecular hydride transfer from a metal hydride which is expected to be regenerable from H2 under catalytic conditions. Further, it provides a plausible model for the interaction of [HRu(CO)4] with Ru(CO)4I2 during catalysis, and suggests a possible role for the second equivalent of [HRu(CO)4]- which the kinetics indicate to be involved in the process (see Fig. 23). Since the Ru(CO)4 fragment which would remain after hydride transfer (perhaps reversible) from [HRu(CO)4] is eventually converted to [HRu3(CO)),] [as in (64)] by reaction with further [HRu(CO)4], the second [HRu(CO)4]- ion may be involved in a kinetically significant trapping reaction. 

III. Physical Properties of Transition Metal Formyl Complexes. 13... 

Possible routes (i) hydrolysis of thioformyl or similar derivative (ii) dealkylation of M=CHOR carbenes Scheme 1. Some synthetic approaches to transition metal formyl complexes. 

All anionic transition metal formyl complexes described in the literature through the end of 1980 (21-47) are compiled in Table I. Since several of these have been prepared with more than one counterion, cations are not specified in the table. Geometric isomers are not assigned unless warranted by direct spectroscopic evidence. Also, the stability data in Table 1 should be regarded as qualitative, since decomposition rates have been shown to be dependent on both purity and counterion. When half-lives are specified, they are usually based upon measured rate constants. 

All neutral transition metal formyl complexes described in the literature through the end of 1980 (52-68) are compiled in Table II. General comments made in the previous section regarding Table 1 apply. 

PHYSICAL PROPERTIES OF TRANSITION METAL FORMYL COMPLEXES... 

Transition metal formyl complexes are capable of donating hydride to several classes of substrates, of which ketones and aldehydes are pro-... 

It is evident that transition metal formyl complexes possess a unique and rich chemistry. There are numerous surprising contrasts to reactions of transition metal acyl complexes. Since synthetic routes to formyl com-... 

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