Synthesis, Structures, and Electrochemistry of Group 6 Aminocarbenes with a P-Chelating 1‘-(Diphenylphosphino)ferrocenyl Substituent

Abstract

Ferrocene amides Ph2PfcC(O)NR2 (1; fc = ferrocene-1,1‘-diyl, NR2 = NEt2 (a), morpholin-4-yl (b)) react with [Cr(CO)5]2- in the presence of Me3SiCl to give easily separable mixtures of the respective P-chelated carbene [Cr(CO)4(Ph2PfcC(NR2)-κ2C1,P)] (2) and a phosphine complex, [Cr(CO)5(1-κP)] (3). A similar reaction between 1a and [W(CO)5]2- is more complex, affording a mixture of the nonchelated carbene [Cr(CO)4{Ph2PfcC(NEt)2-κC1}] (5), trimetallic carbene [(μ-1κC1,2κP-Ph2PfcC(NEt2)){W(CO)5}2] (6), and the phosphine complex [W(CO)5{1a-κP}] (4). Removal of 4 by chromatography and heating the mixture of 5 and 6 in toluene gives another mixture containing carbene analogous to 2, [W(CO)4(Ph2PfcC(NEt2)-κ2C1,P)] (7), unreacted 6, and [W(CO)5{Ph2PfcCHO-κP}] (8) as a decomposition product. In contrast, the reaction of 1a with the iron carbonylate [Fe(CO)4]2- under identical conditions yields solely [Fe(CO)4{1a-κP}] (9). All compounds except for 5 were isolated and characterized by spectral methods. The structures of 2a·CH2Cl2, 2b, 6·CHCl3, 7, and 9 were determined by single-crystal X-ray diffraction. An electrochemical study showed that whereas compounds 1 and 3 behave as a simple system (ferrocene) and two localized redox systems (ferrocene and chromium), respectively, carbenes 2 are electronically delocalized systems, where the redox changes probably occur in the whole molecule.