Synthesis, Characterization, and Reactivity of Isocyanidephosphidoniobocene Derivatives:  X-ray Diffraction Structures of New Isocyanideniobocene Complexes, [Nb(η⁵-C₅H₄SiMe₃)₂(CNR)(PMePh₂)]I, R = Xylyl, Cy

Abstract

The reaction of the hydride niobocene complexes [Nb(η 5 -C 5 H 4 SiMe 3 ) 2 H(L)] [L ) CNBu n (1), CNCy (2), and CNXylyl (3)] with ClPPh 2 yielded the cationic niobocene complexes [Nb(η 5 -C 5 H 4 SiMe 3 ) 2 (PHPh 2 )-(L)]Cl [L ) CNBu n (4), CNCy (5), and CNXylyl ( 6)]. Treatment of these complexes with NaOH yielded a new family of phosphidoniobocene derivatives [Nb(η 5 -C 5 H 4 SiMe 3 ) 2 (PPh 2 )(L)] [L ) CNBu n (7), CNCy (8), and CNXylyl ( 9)] by elimination of the hydrogen atom directly bonded to the phosphorus. The cationic d 2 species [Nb(η 5 -C 5 H 4 SiMe 3 ) 2 (PRPh 2 )(L)]X [R ) Me, X ) I, L ) CNBu n (10), CNCy (11), and CNXylyl (12); R ) CH 2 Ph, X ) Br, CNBu n (13), CNCy ( 14), and CNXylyl (15); R ) CH 2 CH 2 Ph, X ) Br, CNBu n (16), CNCy (17), and CNXylyl (18)] were prepared by the reaction of alkyl halides RX (R ) Me, X ) I; CH 2 Ph, X ) Br; CH 2 CH 2 Ph, X ) Br) with 7, 8, or 9 by electrophilic attack on the phosphorus atom present in the phosphido terminal ligand. In the same way, the reaction of 9 with ICH 2 CH 2 I or iodine yielded the complex [Nb(η 5 -C 5 H 4 SiMe 3 ) 2 (P(I)Ph 2 )(CNXylyl)]I 3 (19). The insertion reaction of carbon disulfide into the Nb-P bond of 7, 8, or 9 yielded a new family of diphenylphosphidodithioformato complexes with the niobocene system [Nb(η 5 -C 5 H 4 SiMe 3 ) 2 (κ 1 -S-SC(S)(PPh 2 ))(L)] [L ) CNBu n (20), CNCy (21), and CNXylyl ( 22)]. The molecular structures of 11 and 12 were determined by single-crystal X-ray diffraction studies.

Insertion Reactions of Isothiocyanates into the Nb–P Bond of Phosphide–Niobocene Complexes

“…[4,5] In this context, our research group has previously reported the synthesis of new phosphido-containing niobocene complexes, and the insertion reaction of carbon disulfide into their Nb-P bond was studied. [6,7] The study of this reactivity allowed us to prepare a series of new niobocene complexes containing the anionic diphenylphosphanylthioformato ligand Ph 2 PCS 2 -, κ 1 -and κ 2 -S-coordinated to the niobium center. These compounds represent good examples of the formation of a carbon-phosphorus bond mediated by transition-metal complexes.…”

“…[8] More recently, we described the preparation of the niobacycles [Nb(η 5 -C 5 H 4 SiMe 3 ) 2 (η 1 -C-C{=N(Xylyl)}C(CO 2 -Me)=C(R)(PPh 2 )-κ 1 -P)] by the insertion reaction of electron-deficient alkynes into the Nb-P bond. [9] We subsequently became interested in studying the reactivity of the Nb-P bond in [Nb(η 5 -C 5 H 4 SiMe 3 ) 2 (PPh 2 )(L)] {L = CO (1), [6] CNXylyl (2), and CNCy (3) [7] } towards isothiocyanates. It is well known that the isothiocyanate functional group R-N=C=S has very interesting reactivity towards alkyl and arylphosphanes to give N-alkylated derivatives in which the phosphorus atom is bonded to the carbon atom to produce phosphanylthioformamide derivatives, particularly when a trimethylsilyl (TMS) group is incorporated into the phosphane or when a secondary phosphane is use in the process (Scheme 1).…”

“…[12] However, to the best of our knowledge a phosphanylthioformamideniobium complex has not been reported in the literature. [13] Herein, we report the synthesis of new phosphanylthioformamide niobocene complexes from phosphido complexes [Nb(η 5 -C 5 H 4 SiMe 3 ) 2 (PPh 2 )(L)] {L = CO (1), [6] CNXylyl (2), and CNCy (3) [7] } by exploring the possibilities for the insertion reaction into the Nb-P bond using unsaturated isothiocyanates as reagents. This reactivity led to the preparation of new niobocene complexes containing the anionic diphenylphosphanylthioformamide ligand {SC(PPh 2 )-(=NR)} coordinated to the niobium center.…”

“…Polynuclear complexes have been prepared by some of us using this synthesis strategy with carboxylic acid [14] or triazine [15] systems. (1), CNXylyl (2), CNCy [7] (3)} and their reactivity in nucleophilic attack on alkyl halides and in the insertion reaction of carbon disulfide (CS 2 ). [6,7] The work described herein concerns the study of the reactivity of complexes 1-3 towards isothiocyanates.…”

“…(1), CNXylyl (2), CNCy [7] (3)} and their reactivity in nucleophilic attack on alkyl halides and in the insertion reaction of carbon disulfide (CS 2 ). [6,7] The work described herein concerns the study of the reactivity of complexes 1-3 towards isothiocyanates. The reaction of these complexes with the aforementioned reagents enabled the synthesis of new phosphanylthioformamideniobocene derivatives, namely [Nb(η 5 -C 5 H 4 SiMe 3 ) 2 {κ 1 -S-SC(PPh 2 )(=NR)}(L)] {R = tBu, L = CO (4), CNXylyl (5); R = Ph, L = CO (6), CNXylyl (7), CNCy (8)}, which were isolated, after the appropriate workup, as reddish-brown, air-sensitive solids that are soluble in thf and toluene [Equation (1)].…”