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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 PdClC 6 HMe 2 (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 C 6 H 2 Me 2 (CH 2 Me 2 pz) 2 ( 2 ) and the 1,3,5-tris(pyrazol-1-ylmethyl)benzenes C 6 HMe 2 (CH 2 pz) 3 ( 7 ) and C 6 HMe 2 (CH 2 Me 2 pz) 3 ( 8 ) behave similarly. Reaction of 1 with a (terpyridine)ruthenium reagent ultimately produces the cycloruthenated derivative (tpy)RuC 6 HMe 2 (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)RuC 6 H 2 Me 2 (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 C 6 H 2 (CH 2 pz) 4 ( 12 ) and C 6 H 2 (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 1 H NMR spectra.
Hartshorn et al. (1998) studied this question.