Dialkyl-μ-ethylidene-μ-methylene-Bis[(pentamethylcyclopentadienyl)dichloro-rhodium] (cas 12354-85-7)pentamethylcyclopentadienyl)-dirhodium complexes: synthesis, spectra and decomposition reactions

Add time:08/12/2019    Source:sciencedirect.com

The dialkyl-μ-ethylidene-μ-methylene-bis (pentamethylcyclopentadienyl)-dirhodium complexes [{(C5Me5)Rh}2(μ-CH2)(μ-CHMe) (R)2] (4, PMe; 5, Et; 6, n-Bu; 7, CHCH2; and 8, Z-CHCHMe) have been prepared from RMgBr and [{(C5Me5)Rh}2(μ-CH2)(μ-CHMe)(X)2] (2, X=Cl; 3, X=Br). Structures deduced from the NMR spectra show that the dialkyl complexes can exist in one trans and two cis forms. The decomposition of the dimethyl complex 4 is compared with that of the related di-μ-methylene complex; it reacts readily (30°C, MeCN solution) in the presence of one-electron oxidisers to give propene and methane and a little ethene and some butenes. Mass-spectrometric analysis of the 13C labelling in the organics originating from [{(C5Me5)Rh}2(μ-CH2)(μ-CHMe) (13CH3)2] shows that methane derives from the RhMe, ethene half from the ethylidene and half from coupling of Rh-methyl and a bridging methylene, while the propene arises almost entirely from the ethylidene and a rhodium methyl. The butenes come from coupling of ethylidene, methylene and a Rh-methyl, but only quite small amounts are formed; thus C+C coupling is the major decomposition path for the μ-ethylidenes, in contrast to the di-μ-methylene complexes where C+C+C coupling predominates. The divinyl complex [{(C5Me5)Rh}2(μ-CH2)(μ-CHMe) (CHCH2)2] also underwent internal C+C coupling on reaction with AgBF4 in MeCN to give a mixture of the allyl and methylallyl cations [(C5Me5)Rh(η3-CH2CHCHR)(MeCN)]+ (10, RH; 11, RMe).

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