Reactions of alkynes with phosphido niobocenes: a combined experimental and theoretical study

Antonio Antiñolo; Santiago García-Yuste; Isabel Lopez Solera; Antonio Otero; Juan Carlos Pérez-Flores; Rebeca Reguillo-Carmona; Elena Villaseñor; Eva Santos; Erik Zuidema; Carles Bo

doi:10.1039/B918298E

Reactions of alkynes with phosphido niobocenes: a combined experimental and theoretical study†

Antonio Antiñolo,*^a Santiago García-Yuste,^a Isabel Lopez Solera,^a Antonio Otero,*^a Juan Carlos Pérez-Flores,^a Rebeca Reguillo-Carmona,^a Elena Villaseñor,^a Eva Santos,^b Erik Zuidema^b and Carles Bo*^bc

Author affiliations

* Corresponding authors

^a Department of Inorganic Chemistry, University of Castilla-La Mancha, Ciudad Real, Spain
E-mail: antonio.otero@uclm.es
Fax: +34 926 295318
Tel: +34 926 295300

^b Institute of Chemical Research of Catalonia (ICIQ), Avda dels Països Catalans 16, Tarragona, Spain

^c Department de Química Fisica i Inorgànica, Universitat Rovira i Virgili, Marcel lí Domingo s/n, Tarragona, Spain

Abstract

The reactions of phosphido complexes [Nb(η⁵-C₅H₄SiMe₃)₂(L)(PPh₂)] [L = CO (1), CNxylyl (2), CNCy (3)] with alkynes have been carried out. The new diphenylphosphinoalkenyl niobocene complexes [Nb(η⁵-C₅H₄SiMe₃)₂(η¹-C–C(CO₂CH₃) [double bond, length as m-dash] C(R)PPh₂)(CO)] [R = H (4), CH₃ (5)] and [Nb(η⁵-C₅H₄SiMe₃)₂(η¹-C–C(CO₂R)C(CO₂R)PPh₂)(CO)] [R = CH₃, (6), R = ^tBu, (7)] were successfully synthesized by the reaction of 1 with methyl propiolate (HC [triple bond, length as m-dash] CCO₂CH₃) or methyl 2-butynoate (CH₃CCCO₂CH₃) and dimethyl 2-butynedioate [(CH₃ O₂C)CC(CO₂CH₃)] or di(tert-butyl) 2-butynedioate [(^tBuO₂C)CC(CO₂^tBu)], respectively. However, reaction was not observed with more electron-rich alkynes. Complex 2 reacted with methyl propiolate, methyl 2-butynoate (MeC [triple bond, length as m-dash] CCO₂Me) or di(tert-butyl) 2-butynedioate to give surprising new heteroniobacycle complexes [Nb(η⁵-C₅H₄SiMe₃)₂(η¹-C–C( [double bond, length as m-dash] NXylyl)C(R¹)C(R²)PPh₂-κ¹-P)] [R¹ = H, R² = CO₂Me (8); R¹ = Me, R² = CO₂Me (9); R¹ = CO₂^tBu, R² = CO₂^tBu (10)]. Finally, the phosphido complexes 2 and 3 reacted with phenylacetylene (PhC [triple bond, length as m-dash] CH) to give new diphenylphosphinoalkenyl niobocene derivatives [Nb(η⁵-C₅H₄SiMe₃)₂(η¹-C–C(C₆H₅) [double bond, length as m-dash] C(H)PPh₂)(CNR)] [R = xylyl (11), Cy (12)]. All of these compounds were characterized by NMR spectroscopy and the molecular structure of 8 was determined by single-crystal X-ray diffraction studies. Theoretical studies were also carried out by means of density functional theory (DFT) calculations on the insertions of alkynes into the Nb–P bond in the phosphido niobocenes.