The Influence of Stepwise P-Oxidation on the Coordination and Redox Behavior of W–Bisphosalkyne Complex Ligands

Abstract

The terminal phosphine groups at the tungsten bisphosphine alkyne complex [Tp*W­(CO)­(I)­(η2-C,C′-Ph2PC2PPh2)] (2) {Tp* = hydridotris­(3,4,5-trimethylpyrazolyl)­borate} were selectively oxidized by common methods to form the alkyne complexes 2EE (E = O, S) with either two phosphine oxide or two phosphine sulfide substituents. The respective mono-oxidized analogues 2E (E = O, S) were obtained by subjecting the already oxidized intermediates [Tp*W­(CO)­(I)­(η2-C,C′-Ph2P­(E)­C2H)] 1E (E = O, S) to a late-stage phosphine introduction at the complex template. These modulations of the peripheral alkyne moiety have a clear impact on the redox potential of the metal-based oxidation altering the W­(II/III) potential by +0.1 V on average per oxidized phosphine. In contrast to the comparable redox behavior of 2O and 2S, the coordination behavior of these complex ligands differs substantially. XRD studies show that complex 2 and the sulfide 2S act either as a P,P’- or P,S-chelate ligand leading to the dinuclear complexes [(2)­PdCl2], 3, and [(2S)PdCl2], 3S. In contrast, the corresponding PdCl2 complex of the monoxide 2O is connected by the free phosphine group and the W-bonded iodide as a μ2-bridging ligand leaving the phosphine oxide pending. A similar binding mode was found for the trinuclear gold complex [(2)2Au]­[PF6] (5-PF6). Furthermore, these findings explain the undesired outcome in the reaction of [Pd­(NCMe)4]­[BF4]2 with two equivalents of 2, which resulted in the iodide abstraction product [(2)­PdI2] (4).

Facile Synthesis of a Stable Side‐on Phosphinyne Complex by Redox Driven Intramolecular Cyclisation

“…According to Scheme2 we recently established as trategy for the selectivei ntroduction of phosphine groups into coordinated acetylene in [Tp*W(CO)I(h 2 -C 2 H 2 )] 1 (Tp* = hydridotris(3,4,5trimethylpyrazolyl)borate). [14] Deprotonation of 1 with nBuLi at À78 8Ca nd subsequentt rapping with ClPPh 2 led to 2.A ccording to 1 Ha nd 31 PNMR spectroscopy (d H = 13.4 ppm for the alkyne-H atom and d P = 18.4 ppm) as ingle isomer was obtained showing the phosphine in the proximity to the pyrazole pocket. The modular character allowed the consecutive introductiono fasecond electrophile.…”

“…[11] The zwitterionic nature of l 5 -phosphinines emphasized already by Dimroth [11,30] is indicated by the significant decreaseo ft he CO stretching frequency by around 70 cm À1 resulting from the deprotonation. As reflected in the resonance structures, the negative 17, W1ÀC2 2.0615 17, W1ÀC3 1.984(2), P1ÀC1 1.7440 18, P1ÀC28 1.7864 18, C23ÀC28 1.405(2),C 16ÀC23 1.537(2), C2ÀC161.502(2), C1ÀC2 1.332(2), C2-C16-C17 117.21 14, C2-C16-C23 112.34 14, C17-C16-C23 114.06 (14). Figure 5.…”

“…Due to the propensity of phosphine groups to metal coordination direct preparative use of suitable free alkynes is not feasible, making a stepwise assembly of the ligand at the metal template necessary. According to Scheme we recently established a strategy for the selective introduction of phosphine groups into coordinated acetylene in [Tp*W(CO)I(η 2 ‐C 2 H 2 )] 1 (Tp*=hydridotris(3,4,5‐trimethylpyrazolyl)borate) . Deprotonation of 1 with n BuLi at −78 °C and subsequent trapping with ClPPh 2 led to 2 .…”

“…Alkyne complexes of W II with two donor centresl ike thiolates, amides or phosphines are suitablep latforms fort he formation of polynuclear complexes. [13][14][15] In regard of am etal-template-based phosphinyne complex synthesis we got interested in the combination of a phosphine and ac arbenium substituent at the coordinated alkyne (C). In addition, this assembly seemed attractive as apotential frustrated Lewis pair (FLP).…”

“…In this context, our research is focused on alkyne complexes bearing heteroatom substituents. Alkyne complexes of W II with two donor centres like thiolates, amides or phosphines are suitable platforms for the formation of polynuclear complexes . In regard of a metal‐template‐based phosphinyne complex synthesis we got interested in the combination of a phosphine and a carbenium substituent at the coordinated alkyne ( C ).…”