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

The activation of C-C bond in coordinated M (eta(4) 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(eta(C5R5)-C-5)(eta(4)- NBD] (R = H, CH3) M = Co, Rh,with CF3COOH or CF3SO3 H forms transient agostic metal hydrides (M-H-C) at -80 degrees C. Similar reaction with HPF6 (60% aq), the Ir analogues give terminal hydrides [IrH(eta(5)-C5Me4R)(eta(4) -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 eta(2)-vinyl eta(3) cyclopentenyl cations [M(eta(C5R5)-C-5) (C7H9)] -, (M=Co Rh, Ir). Protonation of the cobalt and rhodium co-ordinated bicyclo-[2.2.2]-octa 2,5- diene gives unstable M-H-C ground state structures at -80 degrees C, which decompose upon warming to room temp. Protonation reactions of the 2,5-BCOD complexes of Ir also give terminal hydrides [IrH(eta(5)-C5Me5)(eta(4)-2,5-BCOD)]+PF6 as (solids). Thermolysis of [IrH(eta(5)-C5Me5)(eta(4)-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 [J(CH)] and stretching frequency [v 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 eta(6)-toluene cations [M(eta(5)-C5R5)(eta(6)-C6H5CH3)(+). At 50 degrees C in vacuo the salt [(eta(5)-C5Me5)Ir(H)(eta(4)nbd]+PF6 forms a neutral tetramethylfulvenyliridium (1) complex eta(C5Me4)-C-5=CH2)Ir(eta(NBD)-N-4) by C-H activation of a methyl group in the C5Me5 ring. (C) 2021 Elsevier B.V. All rights reserved.