Synthesis, coordination and catalytic use of 1-(diphenylphosphino)-1′-carbamoylferrocenes with pyridyl-containing N-substituents

Abstract

Ferrocene phosphinocarboxamides, 1-(diphenylphosphino)-1′-{N-[(2-pyridyl)methyl]carbamoyl}ferrocene (1) and 1-(diphenylphosphino)-1′-{N-[2-(2-pyridyl)ethyl]carbamoyl}ferrocene (2) were prepared from 1-(diphenylphosphino)-1′-ferrocenecarboxylic acid and studied as ligands for palladium. Starting with [PdCl₂(cod)], the reactions at a 2 : 1 ligand-to-metal ratio gave uniformly the bis-phosphine complexes [PdCl₂(L-κP)₂] (3, L = 1; 4, L = 2) whereas those performed at a 1 : 1 ratio yielded distinct products: [PdCl₂(1-κ²P,N)] (5) with 1 coordinating as a trans-spanning P,N-donor, and the symmetric, P,N-bridged dimer [(µ-2-N,P)₂{PdCl₂}₂] (6), respectively. The crystal structures of 1, 2, 4·4CHCl₃, 5·AcOH, and 6·8CHCl₃ as determined by X-ray diffraction showed the compounds to form well defined solid-state assemblies through hydrogen bonds. Testing of the phosphinocarboxamides in the palladium-catalysed Suzuki cross-coupling reaction revealed 1 and 2, combined with Pd(OAc)₂ to form efficient catalysts for the reactions of aryl bromides while aryl chlorides coupled only when activated with electron-withdrawing groups.