Protonation of Group 9 Metal (Co, Rh, Ir) Coordinated Bicyclo-[2.2.1]-hepta-2,5-diene and Bicyclo[2.2.2]octa-2,5-diene complexes: Facile Activation of Carbon-Carbon Bond in Bicyclo-[2.2.1]hepta-2,5-diene via M-H or M-H-C interactions

Abstract

The activation of C-C bond in coordinated M (η4 bicyclo [2.2.1]-hepta-diene) or 2,5-NBD via protonation for 3d,4d and 5d transition metals have been examined. Monoprotonation of the diolefin complexes [M(η5C5R5)(η4- NBD] (R = H, CH3) M = Co, Rh,with CF3COOH or CF3SO3H forms transient agostic metal hydrides (M-H-C) at -80°C. Similar reaction with HPF6 (60% aq), the Ir analogues give terminal hydrides [IrH(η5-C5Me4R)(η4-2,5-NBD)]+PF6 (R=Me, or Et) as isolable solids at room temperature. All these hydride complexes coordinated to NBD subsequently undergo ligand migration to give stable η2-vinyl η3cyclopentenyl cations [M(η5C5R5) (C7H9)]+ (M=Co Rh, Ir). Protonation of the cobalt and rhodium coordinated bicyclo-[2.2.2]-octa 2,5- diene gives unstable M-H-C ground state structures at -80°C, which decompose upon warming to room temp. Protonation reactions of the 2,5-BCOD complexes of Ir also give terminal hydrides [IrH(η5-C5Me5)(η4-2,5-BCOD)]+PF6 as solids. Thermolysis of [IrH(η5-C5Me5)(η4-2,5-BCOD)]+PF6 did not give the expected, isomerized or C-C bond activated product, probably because 2,5-BCOD is less strained than 2,5-NBD. Coupling constant [JCH] and stretching frequency [ν M-H] data indicate the electron density donation from the methyl groups in the Cp ring favors agostic structures. The C-C bond activation in the coordinated norbornadiene, via hydride migration is slower for the terminal hydride, M-H (M= Ir) compared to agostic hydrides for (M=Co, Rh) compounds. The vinyl cyclopentenyl cations of Rh,Ir undergo further isomerization in CF3COOH to give corresponding η6-toluene cations [M(η5-C5R5)(η6-C6H5CH3)]+ At 50 °C in vacuo the salt [(η5C5Me5)Ir(H)(η4nbd]+PF6 forms a neutral tetramethylfulvenyliridium (1) complex η5C5Me4=CH2)Ir(η4NBD) by C-H activation of a methyl group in the C5Me5 ring.