Bis(diethylphosphino)methane As a Bridging Ligand in Complexes of Ir₂, Rh₂, and IrRh: Geminal C–H Activation of α-Olefins

Abstract

Bis­(diethylphosphino)­methane (depm, Et2PCH2PEt2) is used as a new bridging ligand for the syntheses of a series of diiridium, dirhodium, and iridium/rhodium complexes, starting from trans-[MM′Cl2(CO)2(depm)2] (M = M′ = Ir (1); M = M′ = Rh (11); M = Ir, M′ = Rh (19)). The reduction of all three chloro compounds in aqueous KOH under an atmosphere of CO produces the neutral tricarbonyl complexes [MM′(CO)3(depm)2] (M = M′ = Ir (2); M = M′ = Rh (12); M = Ir, M′ = Rh (20)). Protonation of these tricarbonyl complexes by triflic acid (HOTf) or Brookhart’s acid (HBArF 4) yields the hydride-bridged tricarbonyl complexes [MM′(CO)3(μ-H)­(depm)2]­[X] (M = M′ = Ir (9); M = M′ = Rh (16); M = Ir, M′ = Rh (25); X = SO3CF3 or B­(3,5-(CF3)2C6H3)4). Reaction of 2 with methyl triflate yields the methylene/hydride product [Ir2(H)­(CO)3(μ-CH2)­(depm)2]­[OTf] (4), while the same reaction with the dirhodium analogue (12) produces the methyl complex [Rh2(CH3)­(CO)3(depm)2]­[OTf] (14) at below −20 °C, which upon warming to above −20 °C results in migratory insertion to yield an acetyl-bridged species, [Rh2(CO)2(μ-C­(CH3)­O)­(depm)2]­[OTf] (14a). The analogous Rh/Ir species(20) reacts with methyl triflate to give the methyl-tricarbonyl product [IrRh­(CH3)­(CO)3(depm)2]­[OTf] (22). Removal of a carbonyl from 4 and 22 yields [MIr­(CH3)­(CO)2(depm)2]­[OTf] (M = Ir (5); M = Rh (23)), which are highly susceptible to hydrolysis; however the dirhodium species 14 and 14a are not susceptible to CO loss under the conditions investigated. The reaction of [Ir2(CO)3(μ-H)­(depm)2]­[BArF 4] (9) with a number of α-olefins results in double C–H bond activation of the geminal hydrogens to give the vinylidene-bridged trihydride products of the form [Ir2(H)2(CO)2(μ-H)­(μ-CCRR′)­(depm)2]­[BArF 4].

Bis(dimethylphosphino)methane-ligated silver chloride, cyanide and hydride cluster cations: Synthesis and gas-phase unimolecular reactivity

“…As has been noted by other workers [12], the dmpm ligand is challenging to work with due to its pyrophoric nature and stench, and can yield variations in the outcomes for the synthesis of transition metal complexes. Indeed, we found that different syntheses yielded different relative ion intensities depending, amongst others, on the exact concentration of species in solution, the time at which the reaction mixture was analysed and the inertness of the reaction atmosphere used in the synthesis.…”

“…CID of [Ag 2 ClL] + generated the same fragments to those seen in Eqs. (12) and (13) (27)) is predicted to be the most thermodynamically favoured pathway (37 kJ/mol), however, it is a very minor channel experimentally. Conversely, the loss of a ligand (Eq.…”

Methyl Complexes of the Transition Metals

“…Only two cluster‐type molecules exhibiting Ir−CH 3 bonds have been structurally characterized in the last five years by Adams’ group . Research in the field of Ir alkyls is often devoted to the stoichiometric and, in some cases, catalytic activation of C−H, C−C, and C−O inert bonds. A bulky porphyrin Ir III methyl complex has been employed for the catalytic insertion of organic carbenes into C−H and Si−H bonds .…”

Rhodium(ii) dimers without metal–metal bonds

“…True paramagnetic mononuclear complexes of Rh II are relatively rare. [11][12][13][14] In the present paper, we report on what we believe are the first examples of paramagnetic, dimeric true Rh II complexes which do not contain metal-metal bonds. Wellknown examples are quadruply carboxylate 9 and amidinate 10 bridged systems as well as A-frame complexes.…”