Formation of 1,2,3-eta(3)-butadienyl derivatives by photochemical C-H activation of Ir(I)-eta(4)-1,3-diene complexes containing tris(pyrazolyl)borate ligands

Several Ir(I) complexes of composition [Tp'Ir(diene)], where Tp' = hydrotris(1-pyrazolyl)borate, Tp or hydrotis(3,5-dimethyl-1-pyrazolyl)borate, Tp* and diene = conjugated diene, have been prepared by treating [Ir(mu-Cl)(coe)(2)](2) with the appropriate diene and then with KTp'. The series of related complexes [Tp * Ir(eta(4)-2,3-RR' C4H4)] (R, R' = H, 3; R = Me, R' = H, 4; R, R' = Me, 5) has been chosen for comparative studies on photochemical C-H bond activation reactions. These have been demonstrated to occur only at the C-R and C-R' moieties. Both vinylic and allylic (CH3) activations have been found for compound 4 (R = Me, R'= H), while 3 seems to undergo exclusively central C-H vinylic addition to the metal centre with only low efficiency. The dimethyl substituted diene ligand of 5 is readily activated at one of the methyl groups, yielding the hydride-allyl complex [Tp* Ir(H)(eta(3)-CH2C(C(Me)=CH2)CH2)] 11. The thermal activation of C6H6 by compound 5 to give the N-2-bridged binuclear species [Tp * Ir(H)(C6H5)](2)(mu-N-2) 12 is also reported.