Cyclometalated compounds. XI. Single and double cyclometalations of poly(pyrazolylmethyl)benzenes

Six ligands containing 1,3-bis(pyrazol-1-ylmethyl)benzene subunits are shown to readily undergo cyclometalation reactions. 1,3-Bis(pyrazol-1-ylmethyl)-4,6-dimethylbenzene (1) is cyclopalladated to form the complex PdCl[C6HMe2(CH(2)pz)(2)-N, C,N] (3), containing two fused-ring six-membered metallocycles, for which the X-ray crystal structure of the DMSO solvate is described. The tetramethyl-substituted derivative C6H2Me2(CH(2)Me(2)pz)(2) (2) and the 1,3,5-tris(pyrazol-1-ylmethyl)benzenes C6HMe2(CH(2)pz)(3) (7) and C6HMe2(CH(2)Me(2)pz)(3) (8) behave similarly. Reaction of 1 with a (terpyridine)ruthenium reagent ultimately produces the cycloruthenated derivative (tpy)Ru[C6HMe2(CH(2)pz)(2)-N,C,N](+) (6), the hexafluorophosphate salt of which is also crystallographically characterized. This reaction proceeds by way of a novel intermediate dication (tpy)Ru[C6H2Me2(CH(2)pz)(2)-N,N](2+) (5) that is shown, by detailed NMR studies, to contain an aryl C-H ... Ru interaction. The 1,2,4,5-tetrakis(pyrazol-1-ylmethyl)benzenes C6H2(CH(2)pz)4 (12) and C6H2(CH(2)Me(2)pz)(4) (13) undergo single and double cyclopalladation reactions. The X-ray crystal structure of the doubly palladated derivative of 13 is described. In all cases, the six-membered metallocycles exist in boat conformations, which leads to interesting dynamic behavior in their H-1 NMR spectra.