The effect of ancillary ligands on intramolecular protonhydride (NH⋯HIr) bonding in complexes of iridium(III)

The reaction of the trihydride IrH3(PPh3)3 with HBF4 in the presence of pyridinethione (SpyH) affords a dihydrido SpyH complex [IrH2(η1-SpyH)(PPh3)3](BF4) (1). Complex 1 undergoes a substitution of one of the PPh3 ligands by another SpyH to produce [IrH2(η1-SpyH)2(PPh3)2](BF4) (2). Complex 2 slowly eliminates a dihydrogen molecule to form a known monohydrido complex [IrH(η1-SpyH)(η2-Spy)(PPh3)2](BF4) under mild conditions. [IrH(CO)(η1-SpyH)2(PPh3)2](BF4)2 (3) is obtained from the reaction of known IrH3(CO)(PPh3)2 with HBF4 in the presence of SpyH. The properties of the NH⋯HIr protonhydride bonds (also known as dihydrogen bonds) in complexes 1–3 are characterized in solution by T1 NMR measurements and in the solid state by IR measurements and single crystal X-ray diffraction. They are compared with properties of three related complexes to understand the effect of the ancillary ligands on the strength of this non-classical bond. Stronger protonhydride bonds are formed in complexes with PCy3 co-donor ligands in comparison with complexes with PPh3 co-donor ligands. The strength of protonhydride bonds is decreased in complexes containing more PPh3 or CO ligands. The best indicators of H⋯H bond strength are Δν values from IR and the N⋯Ir distance from the X-ray structures.