Chelate Complexes of Functionalized Cycloheptatrienyl Ligands: 17- and 18-Electron Molybdenum Complexes with Linked Cycloheptatrienyl−Phosphane Ligands and Their Use in Transition Metal Catalysis

Abstract

The synthesis of P-functionalized molybdenum chelate complexes incorporating the linked cycloheptatrienyl− phosphane ligand [2-(diphenylphosphanyl)phenyl]cycloheptatrienyl, o-Ph 2 P−C 6 H 4 −C 7 H 6 , is described. The air-stable ligand precursor [2-(cyclohepta-2,4,6-trienyl)phenyl]diphenylphosphane (2) can be obtained in large quantities by addition of lithiated 2-BrC 6 H 4 PPh 2 (1) to the tropylium cation C 7 H 7 + . Hydride abstraction employing the trityl cation, Ph 3 C + , results in the formation of the tricyclic phosphonium salt 3. The P-functionalized cycloheptatriene 2 acts as an eight-electron ligand on reaction with Mo(CO) 6 to afford the cycloheptatriene−phosphane complex [(o-Ph 2 PC 6 H 4 -η 6 -C 7 H 7 )Mo(CO) 2 (P−Mo)] (4) as a single, chiral regioisomer, which undergoes clean hydride abstraction on treatment

Single-crystal EPR study and DFT structure of the [Mo(CO)5PPh3]+· radical cation

“…To this end, we will first show that calculations using Density Functional Theory (DFT) are able to predict the EPR tensors, which were determined, many years ago by Hayes, for the radical anion [Mo(CN) 5 NO] 3À [14]. As far as we know, this complex constitutes, indeed, the single example of a 17-electron Mo complex whose tensors have been obtained from a careful single crystal EPR analysis.…”

“…These species are invoked as intermediates in many syntheses; some of them, for example, have been proposed as catalysts for olefin metathetical polymerization [5], while metal-centred radicals derived from carbonyl complexes, are frequently used for their exceptional substitutional lability [6][7][8]. Intense efforts have been devoted to describe the electronic structure of 17-electron Mo complexes [9][10][11].…”

“…The purpose of the present study is to show that the rather unstable radical cation [Mo(CO) 5 PPh 3 ] + Á can be formed and trapped, at 77 K, in a single-crystal matrix and to get insight into its electronic structure. To this end, we will first show that calculations using Density Functional Theory (DFT) are able to predict the EPR tensors, which were determined, many years ago by Hayes, for the radical anion [Mo(CN) 5 NO] 3À [14].…”

“…As far as we know, this complex constitutes, indeed, the single example of a 17-electron Mo complex whose tensors have been obtained from a careful single crystal EPR analysis. We will then show that the g-tensor, as well as the 31 P and 95/97 Mo hyperfine tensors predicted by DFT for [Mo(CO) 5 PPh 3 ] + Á are consistent with those measured at low temperature with an X-irradiated single crystal of Mo(CO) 5 PPh 3 . Moreover, comparison between the optimized structures of [Mo(CO) 5 PPh 3 ] + Á and [Mo(CO) 5 PH 3 ] + Á will point out the role played by the triphenylphosphine ligand in the electronic structure of the radical cation.…”

“…Calculations at the B3LYP/ZORA/SOMF level of theory show that, in contrast to Mo(CO) 5 PH 3 , one-electron oxidation of Mo(CO) 5 PPh 3 causes an appreciable change in the geometry of the complex. The g-tensor and the 95/97 Mo and 31 P isotropic and anisotropic coupling constants calculated for [Mo(CO) 5 PPh 3 ] + Á confirm the trapping of this species in the irradiated crystal of Mo(CO) 5 PPh 3 ; they also show that the conformational modifications induced by the electron release are probably hindered by the nearby complexes. …”