Reactions of (trimethyltriazacyclononane)Rh(vinyl)(3), -Rh(Z-propenyl)(3),and -Rh(vinyl)(2)Me with protic acids. The relative migratory aptitude of methyl and vinyl groups to an (ethylidene)Rh alkylidene carbon

Preparations of CnRh(CH=CH2)(3), CnRh(Z-CH=CHMe)(3), and CnRhMe(CH=CH2)(2) (Cn = 1,4,7-trimethyl-1,4,7-triazacyclononane) are reported. An X-ray cryst al structure determination of CnRh(CH=CH2)3 revealed Cs molecular symmetry with average lengths Rh-N, 2.25 Angstrom; Rh-C, 2.00 Angstrom; and C=C, 1.3 1 Angstrom. Protonations of these compounds were carried out with HOTf (tri flic acid, HOSO2CF3), [H(Et2O)(2)][BAr4] (BAr4 = ((-))B[3,5-(CF3)(2)C6H3](4 )), and HCl in organic solvents as well as with methanol as solvent and aci d. CnRh(CH=CH2)(3) gave [CnRh(CH=CH2)(eta(3)-E-CH2CHCHMe)]X. in isolated yi elds up to ca. 80%. Use of CD3OD as acid/solvent led to formation of [CnRh( CH=CH2)(eta(3)-CH2CHCHCH2D)]X (X = ((-))OCD3 assumed) as the only isotopome ric product, suggesting [CnRh(=CHCH2D)-(CH=CH2)(2)](+) as a probable interm ediate. No Rh(=CH-CH3) functional group could be detected by NMR at -60 deg rees C or above. Triflic acid protonation of CnRh(Z-CH=CHMe)(3) generated [ CnRh(Z-CH=CHMe)(eta(3)-E,E-MeCHCHCHEt)], establishing that product formatio n is by alkenyl migration and not via an electrocyclic ring closure within the [Rh(=CHEt)(CH=CHMe)](+) moiety. Protonation of CnRhMe(CH=CH2)(2) genera ted [CnRhMe(eta(3)-CH2CHCHMe)](+) as the sole product (96% by NMR). Reactio n of CnRh(CH=CH2)(2)Me in CD3OD generated [CnRhMe(eta(3)-CH2CHCHCH2D)]1(+) as the sole isotopomer. Thus, the migratory competition established between methyl and vinyl groups for migration to the carbene carbon in proposed in termediate [CnRh(=CHMe)(CH=CH2)Me](+) is dominated by the vinyl group.