Diphosphorus-bridged heterometallic anions and hydrides derived from reactions of complex [Mo2Cp2(μ-PCy2)(μ-κ2:κ2-P2)(CO)2]− with precursors of 16-electron metal carbonyl fragments

• One or two 16-electron MLn fragments can bind to the P2 ligand of the title anion.
• Novel P2-bridged anions show fluxional behaviour in solution.
• Protonation of a P2-bridged trinuclear anion results in a P–H–Mo interaction.
• Protonation of P2-bridged anions leads to unsaturated hydride derivatives.

Reaction of the Li+ salt of the title anion with [Fe2(CO)9] or tetrahydrofuran adducts of formula [MLn(THF)] gave the trinuclear species Li[Mo2MCp2(μ-PCy2)(μ-κ2:κ2:κ1-P2)(CO)2Ln], (MLn = Fe(CO)4, MnCp′(CO)2, Mo(CO)5, W(CO)5; Cp′ = η5-C5H4Me), some of which could be isolated as the corresponding PPN+ salts (PPN = N(PPh3)2). These products followed from further coordination of the P2 ligand to the incoming 16-electron MLn fragment via the lone electron pair at its basal P atom, and displayed characteristically high P–P couplings (1JPP ca. 500 Hz) indicative of retention of a strong P–P bond. In addition, these products underwent a fluxional process derived from the swing of the P2 unit around the Mo–Mo axis with concomitant exchange of the MLn fragment between P atoms. Reaction of the title anion with excess of the above carbonyl complexes involved further addition of a second MLn fragment to the P atom still bearing a lone electron pair, thus leading to the tetranuclear anionic derivatives Li[Mo2M2Cp2(μ-PCy2)(μ-κ2:κ2:κ1:κ1-P2)(CO)2L2n], most of which could be isolated as the corresponding PPN+ salts. For the Mo and W derivatives, this reaction also involved a trans to cis isomerisation at the Mo2(CO)2 moiety of the parent anion. All tetranuclear anions displayed fluxional behaviour in solution, comparable to that of the parent anion in the case of the Fe and Mn derivatives, but likely involving rotation of the P2 ligand in the case of the cisoid Mo and W derivatives. Protonation of the above trinuclear anions with [NH4]PF6 led to decomposition except for the Mn complex, this yielding a poorly characterized diphosphenyl derivative [MnMo2Cp2Cp′(μ-κ1,η2:κ2:κ1-HP2)(μ-PCy2)(CO)4] displaying an agostic-like P–H–Mo interaction, eventually decomposing to the known phosphide-bridged complex [MnMo2Cp2Cp′(μ3-P)(μ-PCy2)(CO)4]. In contrast, protonation of the tetranuclear anions yielded the unsaturated hydride derivatives [Mo2M2Cp2(H)(μ-PCy2)(μ-κ2:κ2:κ1:κ1-P2)(CO)L2n], (M = Mn, Mo, W), with a formal intermetallic double bond (Mo–Mo = 2.7412(6) Å for the tungsten complex) as a result of loss of a CO ligand from the Mo2(CO)2 moiety after protonation, probably favoured by the presence of excess of adducts [MLn(THF)] in these reaction mixtures.

Reaction of the title anion with [Fe2(CO)9] or tetrahydrofuran adducts of formula [MLn(THF)] leads to tri- or tetranuclear anions [Mo2MCp2(μ-PCy2)(μ-κ2:κ2:κ1-P2)(CO)2Ln]− or [Mo2M2Cp2(μ-PCy2)(μ-κ2:κ2:κ1:κ1-P2)(CO)2L2n]− respectively. Protonation of the latter anions involves spontaneous decarbonylation of the Mo2(CO)2 moiety to give hydride derivatives [Mo2M2Cp2(H)(μ-PCy2)(μ-κ2:κ2:κ1:κ1-P2)(CO)L2n] having MoMo double bonds.Figure optionsDownload as PowerPoint slide