Journal: Dalton transactions (Cambridge, England : 2003)

Article Title: Dimethylphosphinate bridged binuclear Rh(i) catalysts for the alkoxycarbonylation of aromatic C-H bonds.

PMID/MRN: 27722359

Publication Date: 2016-Nov-14

Abstract:

A variety of binuclear rhodium(i) complexes featuring two bridging dimethylphosphinate ligands ((CH 3 ) 2 PO 2 - ) have been prepared and tested in the alkoxycarbonylation of aromatic C-H bonds. The complex [Rh(?-?O,O'-(CH 3 ) 2 PO 2 )(cod)] 2 has been prepared by a reaction of [Rh(?-MeO)(cod)] 2 with 2 equivalents of dimethylphosphinic acid. Binuclear complexes [Rh(?-?O,O'-(CH 3 ) 2 PO 2 )(CO)L] 2 (L = PPh 3 , P(OMe)Ph 2 and P(OPh) 3 ) were obtained by carbonylation of the related mononuclear complexes [Rh(?O-(CH 3 ) 2 PO 2 )(cod)(L)], which were prepared in situ by the reaction of [Rh(?-?O,O'-(CH 3 ) 2 PO 2 )(cod)] 2 with 2 equivalents of L. Conversely, if L = IPr, the reaction of [Rh(?-?O,O'-(CH 3 ) 2 PO 2 )(CO)L] 2 with carbon monoxide affords the mononuclear complex [Rh(?O-(CH 3 ) 2 PO 2 )(CO) 2 IPr]. The subsequent reaction with trimethylamine N-oxide gives the corresponding binuclear complex [Rh(?-?O,O'-(CH 3 ) 2 PO 2 )(CO)(IPr)] 2 by abstraction of one of the carbonyl ligands. Complexes [Rh(?-?O,O'-(CH 3 ) 2 PO 2 )(cod)] 2 and [Rh(?O-(CH 3 ) 2 PO 2 )(cod)(L)] (L = IPr, PPh 3 , P(OMe)Ph 2 , P(OPh) 3 ) are active precatalysts in the alkoxycarbonylation of C-H bonds, with the ligand system playing a key role in the catalytic activity. The complexes that feature more labile Rh-L bonds give rise to better catalysts, probably due to the more straightforward substitution of L by a second carbonyl ligand, since a more electrophilic carbonyl carbon atom is more susceptible toward aryl migration. In fact, complexes [Rh(?-?O,O'-(CH 3 ) 2 PO 2 )(CO) 2 ] 2 and [Rh(?-Cl)(CO) 2 ] 2 , generated in situ from [Rh(?-?O,O'-(CH 3 ) 2 PO 2 )(cod)] 2 and [Rh(?-Cl)(cod) 2 ] 2 , respectively, are the most active catalysts tested in this work.