Formation of octahedral iridium(III) dihydrides from the reaction of ortho-chelated aryliridium(I) compounds with dihydrogen

The reaction of Ir/sup I/(CH/sub 2/NMe/sub 2/)-2-R/sup 1/-4-R/sup 2/-6)(COD) (COD = cyclooacta-1,5-diene) with dihydrogen in CD/sub 2/Cl/sub 2/ was monitored by /sup 1/H NMR. At -20/sup 0/C quantitative formation of the novel dihydride complexes Ir/sup III/H/sub 2/(C/sub 6/H/sub 2/(CH/sub 2/NMe/sub 2/)-2-R/sup 1/-4-R/sup 2/-6)(COD) (R/sup 1/ = H, R/sup 2/ = CH/sub 2/NMe/sub 2/ (10), Me (11); R/sup 2/ = H, R/sup 1/ = H (12), Me (13), CH/sub 2/NMe/sub 2/ (14); R/sup 1/ = R/sup 2/ = CH/sub 2/NMe/sub 2/ (15)) occurs. Further reactions, the type of which depends on the bulkiness of the R/sup 1/ and R/sup 2/ groups, occur when these solutions are warmed to 0/sup 0/C. Complexes 12-14 (R/sup 2/ = H) lose H/sub 2/ to re-form Ir/sup I/(C/sub 6/H/sub 3/(CH/sub 2/NMe/sub 2/)-2-R/sup 1/-4)(COD). In contrast, complexes 10, 11, and 15 (R/sup 2/ = alkyl) react further by means of C(aryl)-H reductive elimination. For complex 15 (R/sup 1/ = CH/sub 2/NMe/sub 2/) this results in quantitative formation of 1,3,5-(Me/sub 2/NCH/sub 2/)/sub 3/C/sub 6/H/sub 3/ and IrH(COD). In Ir/sup III/H/sub 2/(C/sub 6/H/sub 3/(CH/sub 2/NMe/sub 2/)-2-R-6)(COD) (R = alkyl (10 and 11)), C(aryl)-H reductive elimination is followed by re-addition of another C(aryl)-H bond, which upon subsequent reductive elimination of H/sub 2/, yields the rearranged iridium(I) complexes Ir/sup I/(C/sub 6/H/sub 3/(CH/sub 2/NMe/sub 2/)-2-R-4)(COD). Since the rearrangement of Ir/sup I/(C/sub 6/H/sub 3/-(CH/sub 2/NMe/sub 2/)-2-R-6)(COD) to Ir/sup I/(C/sub 6/H/sub 3/(CH/sub 2/NMe/sub 2/)-2-R-4)(COD) can also be induced thermally at 60/sup 0/C, it is therefore being catalyzed by dihydrogen at 0/sup 0/C. None of these reactions with dihydrogen is attended by hydrogenation of the COD ligand.