From alkynes to carbenes mediated by [Re(Br)(H)(NO)(PR3)2] (R = Cy, iPr) complexes

Abstract

Five-coordinate rhenium(I) hydride complexes of the type [Re(Br)(H)(NO)(PR3)2] (R = Cy 1a, iPr 1b) were reacted with terminal alkynes R1C≡CH (R1 = Ph, SiEt3, H), yielding 18-electron η2-alkyne adducts [Re(Br)(H)(NO)(PR3)2(η2-HC≡CR1)] (R1 = Ph (R = Cy 2a, iPr 2b), SiEt3 (R = Cy 4a, iPr 4b), H (R = Cy 6a, iPr 6b)). Alkyne insertion into the Re−H bond led to the formation of rhenium(I) η1-vinyl derivatives [Re(Br)((E)-CH═CHR1)(NO)(PR3)2] (R1 = Ph (R = Cy 3a, iPr 3b), SiEt3 (R = Cy 5a, iPr 5b), H (R = Cy 7a, iPr 7b)) in good yields. The rate of formation of the vinyl complexes depends on R1 in the order SiEt3 > Ph > H, and the reactions of 1b bearing the PiPr3 ligand are generally faster than those of 1a with PCy3. 1a,b were also reacted with 2-methyl-1-buten-3-yne and 1,7-octadiyne, affording dienyl derivatives [Re(Br){(E)-CH═CHC(CH3)═CH2}(NO)(PR3)2] (R = Cy 8a, iPr 8b) and the binuclear μ-bis-alkenyl compounds [(PR3)2(NO)(Br)Re{(E)-CH═CH-(CH2)4-CH═CH-(E)}Re(Br)(NO)(PR3)2] (R = Cy 9a, iPr 9b). The reactions of 3a,b or 5a,b with HBF4·OEt2 afforded the rhenium(I) carbene derivatives [Re(F)(Br)(═CHCH2Ph)(NO)(PR3)2] (R = Cy 10a, iPr 10b) or [Re(F)(Br)(═CHCH═C(CH3)2)(NO)(PR3)2] (R = Cy 11a, iPr 11b) via protonation at the β- and δ-carbon of the vinyl group, respectively. The fluorine ligands are located cis to the carbene ligand and the bromo atom cis to the nitrosyl group. The binuclear species 9a,b were also reacted with HBF4·OEt2 to afford the binuclear carbene derivatives [(PR3)2(NO)(Br)(F)Re{═CH-(CH2)6-CH═}Re(F)(Br)(NO)(PR3)2] (R = Cy 12a, iPr 12b). The molecular structures of 3a, 5a, and 11a were established by X-ray diffraction studies.