Photochemical Reactivity of Group 9 Metal Pinacolate Complexes

Abstract

Coordinatively unsaturated pentamethylcyclopentadienyl pinacolate complexes of the group 9 transition metals (4-6) have been prepared and characterized. Photolysis of either the cobalt complex 4 or the rhodium complex 5 results in cleavage of the central carbon-carbon bond in the diolate, generating acetone. Various trapping studies demonstrate that an intact [Cp*M] fragment is produced in these reactions, and in the absence of added traps this fragment reacts either with aromatic solvents or with an intact molecule of the starting pinacolate complex. The oxidation of the resulting rhodium(II) product 11 by air (or O 2 ) in the presence of pinacol regenerates the rhodium(III) pinacolate complex 5. Photolysis of rhodium complex 5 in the presence of pinacol and oxidant (either O 2 or N 2 O) results in the catalytic conversion of pinacol to acetone.

Characterization of an activated iridium water splitting catalyst using infrared photodissociation of H2 tagged ions

“…27 Upon loss of the Cl À to form the activated species, the remaining ligands are predicted to rearrange into a slightly distorted trigonal planar coordination geometry, which is consistent with experimental geometries observed for related iridium dialkoxides. 32,33 The harmonic spectrum (scaled by 0.96) calculated for this (bare) structure is shown in Fig. 2b, and is in remarkable agreement with that recorded by predissociation of the H 2 adducts (Fig.…”

Dihydrogen Catalysis of the Reversible Formation and Cleavage of CH and NH Bonds of Aminopyridinate Ligands Bound to (η5‐C5Me5)IrIII

“…Moreover, the very dark colour of these cations has been previously observed for complexes with MN and MO bonds stabilised by π donation and has been attributed to ligand‐to‐metal charge‐transfer π→d electronic transitions 6a–e. 17, 26, 27…”

“…Moreover, the very dark colour of these cations has been previously observed for complexes with MÀN and MÀO bonds stabilised by p donation and has been attributed to ligand-to-metal charge-transfer p!d electronic transitions. [6a-e, 17, 26,27] The neutral complexes 1 a·Cl-1 d·Cl and their corresponding cationic derivatives 1 a + -1 d + were characterised by conventional structural techniques. 1 H and 13 C NMR spectroscopic studies (1D and 2D experiments) provide convincing evidence for the formulation proposed in Scheme 3.…”

Synthesis and structure of “16-electron” rhodium(iii) catalysts for transfer hydrogenation of a cyclic imine: mechanistic implications

“…Related complexes with M-O bonds are also stabilised by p-donation. 4,6 When one of the NH groups is tosylated, the bonding of the NTs and NH groups may be significantly different. 7 Protonation of Cp*Ir(TsNCHPhCHPhNH) at the NH group results in elongation of the Ir-NH bond and contraction of the Ir-NTs bond, indicating redirection of p-bonding from one nitrogen to the other.…”