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Reactions of alkyl and hydride derivatives of permethylzirconocene and permethylhafnocene with carbon monoxide. Synthesis and reactivity studies of aldehyde complexes of zirconium and hafnium
Author(s) -
Roddick Dean M.,
Bercaw John E.
Publication year - 1989
Publication title -
chemische berichte
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 0009-2940
DOI - 10.1002/cber.19891220829
Subject(s) - chemistry , hydride , adduct , medicinal chemistry , carbonylation , reactivity (psychology) , cyclopentanone , aldehyde , alkyl , carbon monoxide , stereochemistry , organic chemistry , hydrogen , catalysis , medicine , alternative medicine , pathology
The alkyl hydride derivatives Cp 2 * M(H)(CH 2 CHMe 2 ) (Cp * = η 5 ‐C 5 Me 5 , M = Zr, Hf) react with carbon monoxide at low temperature to yield the η 2 ‐acyl hydride complexes Cp 2 * M(H)(η 2 ‐COCH 2 CHMe 2 ) ( 1a , b ), which on warming to room temperature under CO afford the carbonyl/isovaleraldehyde adducts Cp 2 * M(CO)(η 2 ‐OCHCH 2 CHMe 2 ) ( 4a , b ). The zirconium derivative 4a slowly loses its coordinated CO and rearranges to the enolate hydride Cp 2 * Zr(H)(OCHCHCHMe 2 ) ( 3 ). By contrast Cp 2 * Hf‐(CO)(η 2 ‐OCHCH 2 CHMe 2 ) ( 4b ) rearranges without loss of CO to the cyclic enediolate tautomer ( 5 ), most likely by a 1,2H shift from the cyclic acyl derivative . The coordinatively unsaturated η 2 ‐isovaleraldehyde adduct of permethylzirconocene [Cp 2 * Zr(η 2 ‐OCHCH 2 CHMe 2 )] is implicated in reactions of the acyl hydride Cp 2 * Zr(H)(η 2 ‐COCH 2 CHMe 2 ) ( 1a ) with the trapping substrates ethylene, 2‐butyne, dihydrogen, and tert ‐butylacetylene to yield ( 12 ), ( 13 ), Cp 2 * Zr(H)(OCH 2 CH 2 CHMe 2 ) ( 14 ), and Cp 2 * Zr(CCCMe 3 )(OCH 2 CH 2 CHMe 2 ) ( 15 ). Carbonylations of the hafnacyclopentane ( 9 ) and the alkenyl hydride Cp 2 * Hf(H)( trans ‐CHCHCMe 3 ) do not show direct evidence for η 2 ‐cyclopentanone or η 2 ‐aldehyde intermediates. The former does, however, proceed directly to the bicyclic enediolate complex 11 most likely by the subsequent carbonylation of the cyclopentanone adduct. The latter undergoes carbonylation first to the hafna‐oxacyclopentene , which reacts further with CO to yield hafnadioxo‐cycloheptadiene ( 19 ). Possible mechanisms for these processes are discussed. The general natures of this chemistry complement theoretical and experiment results from the Hofmann group presented in the preceding article 17 .