Rhodium Complexes in P−H Bond Activation Reactions

The feasibility of oxidative addition of the P−H bond of PHPh₂ to a series of rhodium complexes to give mononuclear hydrido-phosphanido complexes has been analyzed. Three main scenarios have been found depending on the nature of the L ligand added to [Rh(Tp)(C₂H₄)(PHPh₂)] (Tp= hydridotris(pyrazolyl)borate): i) clean and quantitative reactions to terminal hydrido-phosphanido complexes [RhTp(H)(PPh₂)(L)] (L=PMe₃, PMe₂Ph and PHPh₂), ii) equilibria between Rh^I and Rh^III species: [RhTp(H)(PPh₂)(L)]⇄[RhTp(PHPh₂)(L)] (L=PMePh₂, PPh₃) and iii) a simple ethylene replacement to give the rhodium(I) complexes [Rh(κ²-Tp)(L)(PHPh₂)] (L=NHCs-type ligands). The position of the P−H oxidative addition–reductive elimination equilibrium is mainly determined by sterics influencing the entropy contribution of the reaction. When ethylene was used as a ligand, the unique rhodaphosphacyclobutane complex [Rh(Tp)(η¹-Et)(κ^C,P-CH₂CH₂PPh₂)] was obtained. DFT calculations revealed that the reaction proceeds through the rate limiting oxidative addition of the P−H bond, followed by a low-barrier sequence of reaction steps involving ethylene insertion into the Rh−H and Rh−P bonds. In addition, oxidative addition of the P−H bond in OPHPh₂ to [Rh(Tp)(C₂H₄)(PHPh₂)] gave the related hydride complex [RhTp(H)(PHPh₂)(POPh₂)], but ethyl complexes resulted from hydride insertion into the Rh−ethylene bond in the reaction with [Rh(Tp)(C₂H₄)₂].     

X-Ray Crystal Structures of Two Monopentamethylcyclopentadienylhafnium(IV) Complexes

Crystallography Reports - The crystal structures of two monopentamethylcyclopentadienylhafnium(IV) derivatives have been determined by X-ray diffraction analysis. The [Hf(η5-C5Me5)Cl3] complex...     

Three-Coordinate Rhodium Complexes in Low Oxidation States

The isolation of simultaneously low-coordinate and low-valent compounds is a timeless challenge for preparative chemists. This work showcases the preparation and full characterization of tri-coordinate rhodium(-I) and rhodium(0) complexes as well as a rare rhodium(I) complex. Reduction of [{Rh(μ-Cl)(IPr)(dvtms)}₂] ( 1 , IPr=1,3-bis(2,6-diisopropylphenyl)imidazolyl-2-ylidene; dvtms=divinyltetramethyldisiloxane) with KC₈ gave the trigonal complexes K[Rh(IPr)(dvtms)] and [Rh(IPr)(dvtms)], whereas the cation [Rh(IPr)(dvtms)]⁺ results from their oxidation or by abstraction of chloride from 1 with silver salts. The paramagnetic Rh⁰ complex is a unique fully metal-centered radical with the unpaired electron in the d_z2 orbital. The Rh(-I) complex reacts with PPh₃ with replacement of the NHC ligand, and behaves as a nucleophile, which upon reaction with [AuCl(PPh₃)] generates the trigonal pyramidal complex [(IPr)(dvtms)Rh-Au(PPh₃)] with a metal–metal bond between two d¹⁰ metal centers.     

Isolation of Bis- and Mono-Cyclometallated Ru−IMes Complexes upon Reaction of [Ru(PPh3)3HCl], IMes and ZnMe2

Addition of an excess of ZnMe₂ to a mixture of [Ru(PPh₃)₃HCl] and IMes (IMes=1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene) yields the bis-cyclometallated complex, [Ru(IMes)“(PPh₃)₂] 2 , together with the mono-cyclometallated, Ru−Zn heterobimetallic complex [Ru(IMes)′(PPh₃)₂(ZnMe)] 3 . Treatment of 2 with H₂, PhSiH₃ or pinacolborane yields the previously reported complex, [Ru(IMes)′(PPh₃)₂H] 1 , the synthesis of which has been reinvestigated. Further studies of small molecule reactivity show that 1 adds H₂ to give [Ru(IMes)(PPh₃)₂H₄] 4 , whilst 2 reacts with catecholborane to give [Ru(IMes-Bcat)′(PPh₃)₂H] 5 , in which (IMes-Bcat)′ signifies a borylated NHC ligand that is singly-metallated onto Ru. Treatment of 2 with CO gives the 18-electron dicarbonyl product [Ru(IMes)”(PPh₃)(CO)₂] 6 . Compounds 1 – 3 , 5 and 6 have been structurally characterised.