SYNTHESIS, REACTIVITY, AND STRUCTURE OF 4-COORDINATE (VINYLVINYLIDENE)RHODIUM AND 5-COORDINATE AND 6-COORDINATE ENYNYL(HYDRIDO)RHODIUM COMPLEXES WITH [RHCL(PIPR3)2] AS A MOLECULAR UNIT

The reaction of [RhCl(C8H14)2]2 (4) with PiPr3 and enynes HC=CC(R)=CH(R') [R = R'= H; R = CH3, R' = H; R = H, R' = OCH3] leads to the formation of either (enyne)- or enynyl(hydrido)rhodium complexes (5a,b, 6c) as the first isolable products. At 25-45-degrees-C in toluene, trans-[RhCl(HC=CC(R)=CH2)(PiPr3)2] (5a,b) and [RhH{C=CCH=CH(OCH3)}Cl(PiPr3)2] (6C) smoothly rearrange to give the isomeric (vinyl-vinylidene)rhodium derivatives trans-[RhCl{=C=CHC(R)=CH(R')}(PiPr3)2] (7a-c) in nearly quantitative yield. The parent complex 7a (R = R' = H) has also been prepared from 4, PiPr3, and the alkynol HC=CCH(CH3)OH via the substituted rhodium vinylidene complex trans-[RhCl{=C=CHCH(CH3)-OH}(PiPr3)2] (9), which undergoes elimination of water on treatment with acidic Al2O3 or traces of HX. Both 5a,b and 6c as well as the vinylvinylidene complexes 7a-c react with pyridine at room temperature to give the octahedral rhodium(III) compounds [RhH(C=C(R)=CH(R')}Cl(py)(PiPr3)2] (11a-c). In contrast, the reaction of 7b with CO affords, instead of [RhH{C=CC(CH3)=CH2}CI(CO)(PiPr3)2], the four-coordinate carbonyl complex trans-[RhCl(CO)(PiPr3)2] (13) and free enyne HC=CC(CH3)=CH2. Protonation of 7b with HBF4 gives the cationic carbyne rhodium derivative trans-[RhCl{=CCH=C-(CH3)2}(PiPr3)2]BF4 (14), which on treatment with NaH re-forms the vinylvinylidene compound 7b. The molecular structures of 7b and 11b have been determined. Crystallographic data are as follows: 7b, monoclinic space group P2(1)/c (No. 14) with a = 8.117 (3) angstrom, b = 38.946 (9) angstrom, c = 17.597 (6) angstrom, beta = 93.99 (1)-degrees, V = 5590 angstrom3, and Z = 8; 11b, triclinic space group P1BAR (No. 2) with a = 9.3103 (5) angstrom, b = 11.7936 (8) angstrom, c = 15.322 (2) angstrom, a = 93.246 (7)-degrees, beta = 92.832 (6)-degrees, gamma = 108.981 (5)-degrees, V = 1584 angstrom3; and Z = 2.