Abstract
Although the pentacoordinated complex [Ir{(allyl)B(CH~2~PPh~2~)(pz)~2~}(cod)] (1; pz=pyrazolyl, cod=1,5‐cyclooctadiene), isolated from the reaction of [{Ir(μ‐Cl)(cod)}~2~] with [Li(tmen)][B(allyl)(CH~2~PPh~2~)‐ (pz)~2~] (tmen=N,N,N′,N′‐tetramethylethane‐1,2‐diamine), shows behavior similar to that of the related hydridotris(pyrazolyl)borate complex, the carbonyl derivatives behave in a quite different way. On carbonylation of 1, the metalmetal‐bonded complex [(Ir{(allyl)B(CH~2~PPh~2~)(pz)~2~}CO)~2~(μ‐CO)] (2) that results has a single ketonic carbonyl bridge. This bridging carbonyl is labile such that upon treatment of 2 with PMe~3~ the pentacoordinated Ir^I^ complex [Ir(CO){(pz)B(η^2^‐CH~2~CHCH~2~)(CH~2~PPh~2~)(pz)}(PMe~3~)] (3) was isolated. Complex 3 shows a unique fac coordination of the hybrid ligand with the allyl group η^2^‐bonded to the metal in the equatorial plane of a distorted trigonal bipyramid with one pyrazolate group remaining uncoordinated. This unusual feature can be rationalized on the basis of the electron‐rich nature of the metal center. The related complex [Ir(CO){(pz)B(η^2^‐CH~2~CHCH~2~)(CH~2~PPh~2~)(pz)}(PPh~3~)] (4) was found to exist in solution as a temperature‐dependent equilibrium between the cis‐pentacoordinated and trans square planar isomers with respect to the phosphorus donor atoms. Protonation of 3 with different acids is selective at the iridium center and gives the cationic hydrides [Ir{(allyl)B(CH~2~PPh~2~)(pz)~2~}(CO)H(PMe~3~)]X (X=BF~4~ (5), MeCO~2~ (6), and Cl (7)). Complex 7 further reacts with HCl to generate the unexpected product [Ir(CO)Cl{(Hpz)B(CH~2~PPh~2~)(pz)CH~2~CH(Me)}(PMe~3~)]Cl (9; Hpz=protonated pyrazolyl group) formed by the insertion of the hydride into the Ir(η^2^‐allyl) bond. In contrast, protonation of complex 4 with HCl stops at the hydrido complex [Ir{(allyl)B(CH~2~PPh~2~)(pz)~2~}(CO)H(PPh~3~)]Cl (8). X‐ray diffraction studies carried out on complexes 2, 3, and 9 show the versatility of the hybrid scorpionate ligand in its coordination.