Platinum ethyl complexes with β-agostic Pt–H–C bonding

Abstract

le] and [PtEt,( L-L)] 2a-2d affords a series of cationic platinum(ii) complexes 3a-3e which in the case of 3a-3c adopt a cis ethene/hydride ground state whereas in 3d and 3e the otherwise electron-deficient metal centre is stabilized by a two-electron, three-centre agostic interaction with the P-CH bond of the ethyl ligand. Complexes 1-3 were characterized by 'H, 13C and 31P NMR spectroscopy and for 2d and 3d by single-crystal X-ray crystallography. The influence of the chelating diphosphine ligand on the strength of the agostic bond was monitored b y NMR spectroscopy. This revealed that the cations undergo t w o fluxional processes in solution: (a) agostic methyl rotation and ( b ) 0-elimination/ethene rotation, a combination of which scrambles all five protons and both carbon atoms of the ' C, H, ' moiety. The 31P nuclei, however, remain inequivalent at temperatures u p t o 300 K.The agostic interaction was displaced by a small two-electron donor molecule L t o form the series of adducts [PtEt(L)(L-L)]+ ( L = acetonitrile or pyridine) in which the 'normal' ethyl complex is the first formed species. The adducts are unstable t o loss of C, H, by p-elimination t o form the series of cationic hydrides [PtH( L) (L-L)] +. For comparison, the complex [PtH (0,SCF,){Bu',P(CH,),PBut2}] was synthesised and characterized by H and 31P NMR spectroscopy and X-ray crystallography.104

Rhodium and Iridium β-Diiminate Complexes – Olefin Hydrogenation Step by Step

“…Moreover, the methylene carbon is seen to be coupled to both hydrogens (J ϭ 108 and 141 Hz), but shows no measurable coupling to Rh. Close approach of an NBE methylene hydrogen to a metal has also been observed in [17] but in the three other NBE complexes for which X-ray structures have been reported the distances between the metal and the methylene bridges are much larger: [18] Pt(NBE) 3 (PtC ϭ 3.20/3.13/3.16 Å , PtH ϭ 2.65/ 2.80/3.01 Å ), [19] and a dicopper complex (CuC ϭ 2.96/2.97 Å , CuH ϭ 2.50/2.51 Å ). [20] The observation of a pronounced agostic interaction in L Me Rh(NBE) provides little information concerning the strength of this interaction.…”

Stereoselectivity in the Rhodium‐Catalysed Reductions of Non‐Conjugated Dienes

“…[22] These include at least one example for which the bridging methylene group provides an agostic C À H interaction with the metal centre, [23] and one with an agostic Pt À H À C1 arrangement. [24] The variable behaviour of NDB 1 is more intriguing. Preferred bidentate endo-coordination of NBD in transition metal complexes is well established, and exemplified in the common precatalysts for rhodium asymmetric hydrogenation.…”

T‐Shaped Platinum Boryl Complexes: Synthesis and Structure

“…Such 14-electron platinum(II) compounds are very important owing to their central role in alkane C À H activation, [10] or as models for intermediates in the olefin polymerization catalyzed by late transition metals. [11] Of this kind of Pt species only a handful have been reported, as they are often transient or contain coordinated solvent molecules. Presumably, bulky ligands are necessary to protect the free coordination site to isolate stable 14-electron T-shaped Pt II compounds.…”