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Methylene Transfer from SnMe Groups Mediated by a Rhodium(I) Pincer Complex: SnC, CC, and CH Bond Activation
Author(s) -
Frech Christian M.,
Shimon Linda J. W.,
Milstein David
Publication year - 2007
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200700320
Subject(s) - chemistry , methylene , medicinal chemistry , pincer movement , reactivity (psychology) , bond cleavage , transmetalation , photochemistry , rhodium , stereochemistry , catalysis , organic chemistry , medicine , alternative medicine , pathology
The PCP‐Rh I complex 1 a based on the [1,3‐phenylenebis(methylene)]bis(diisopropylphosphine) ligand reacts with [diazo(phenyl)methyl]trimethylstannane ( 2 ) at room temperature to give novel pincer‐type phenyl(dimethylstannyl)methylene]hydrazinato complex 3 a . The reaction sequence involves a unique combination of SnC bond cleavage, CC bond formation, CH activation and intramolecular deprotonation of a rhodium hydride intermediate, which results in methylene transfer from an SnMe group to the pincer system and PCP‐chelate expansion. A methylene‐transfer reaction was also demonstrated with tetramethyltin as the methylene source in the presence of KOC(CH 3 ) 3 at room temperature. The resulting unstable “chelate‐expanded” Rh I complex [(C 10 H 5 (CH 2 P i Pr 2 ) 2 )(CH 2 )Rh(L)] (L=N 2 , THF; 4 a ) was isolated as its carbonyl derivative 5 a . Heating 4 a in benzene yielded an equimolar amount of toluene and 1 a , which demonstrates the ability of the Rh I pincer complex to extract a methylene group from an unactivated alkyl tin substrate and transfer it, via CC followed by CH activation, to an arene. Use of fluorobenzene resulted in formation of fluorotoluene. Catalytic methylene‐group transfer mediated by 1 a was not possible, because of formation of o ‐xylylene complex 8 under the reaction conditions. Steric parameters play a decisive role in the reactivity with tin compounds; while i PrP derivative 1 a underwent facile reactions, t BuP complex 1 b was inert.