Divergent Reactivity of a Phosphinidene-Bridged Dimolybdenum Complex Toward 1-Alkynes: P–C, P–H, C–C, and C–H Couplings

Abstract

The ability of complex [Mo 2 Cp 2 {μ-P(2,4,6-C 6 H 2 t Bu 3 )}(CO) 4 ] to promote P−C and subsequent coupling processes has been analyzed by examining reactions with alkynes. The title compound reacted at room temperature with different terminal alkynes HCCR under visible-UV light irradiation to give, in a selective way, the corresponding phosphapropenediyl derivatives [Mo 2 Cp 2 (μ−κ 1 C :η 3 C,C,P -CRCHPR*)(CO) 4 ] for R groups of varied electron-withdrawing nature, but low to medium size, such as Pr, CO 2 Me, and p-tol. These products follow from formal insertion of the alkyne into one of the Mo-phosphinidene bonds in the parent compound, with selective P−C coupling to the terminal carbon of the alkyne. In contrast, when R was the bulky t Bu group, the corresponding photochemical reactions yielded a mixture of the cis and trans isomers of the phosphanyl-and formylalkenyl-bridged complex [Mo 2 Cp 2 {μ−κ 2 C,O :η 2 C,C -CHC( t Bu)C(O)H}{μ-P(CH 2 CMe 2 )-C 6 H 2 t Bu 2 }(CO) 2 ], which follow from a complex reaction sequence involving an H−C(sp 3 ) bond cleavage along with different P−C, P−H, C−C, and C−H bond formation steps. Density functional theory calculations were carried out to rationalize the preceding observations and suggested that an isomer of the parent complex displaying a bent terminal phosphinidene ligand might be involved in all the above photochemical reactions.

Acceptor Behavior and E–H Bond Activation Processes of the Unsaturated Heterometallic Anion [MoReCp(μ-PCy2)(CO)5]−(Mo═Re)

“…M–C β lengths were also longer for the other two complexes with alkenyl ligands bridging over Mo–Re or W–Re bonds which have been structurally characterized so far: the aforementioned [MoReCp­(μ-κ 1 :η 2 -CRCHR)­(μ-PCy 2 )­(CO) 5 ] (π-bound to Mo; Mo–C β = 2.309(3) A) and the cluster [W 2 ReCp*­(μ-κ 1 :η 2 -CHCHPh)­(O)­(CO) 8 ] (π-bound to Re; Re–C β = 2.393 A) . We finally note that dimensions within the formyl-alkenyl chain in anti -10 are comparable to those recently measured for the related dimolybdenum complexes cis - and trans -[Mo 2 Cp 2 {μ-κ 2 C,O :η 2 C,C -CHC­( t Bu)­C­(O)­H}­{μ-P­(CH 2 CMe 2 )­C 6 H 2 t Bu 2 }­(CO) 2 ], which are formed in a multistep process taking place upon photolysis of the phosphinidene complex [Mo 2 Cp 2 (μ-PR)­(CO) 4 ] with HCC t Bu, a matter to be further discussed below (R = 2,4,6-C 6 H 2 t Bu 3 ).…”

“…The building of the bridging hydrocarbyl ligand found in complexes 10 necessarily is a multistep process involving alkenyl–carbonyl coupling and H shifts at some stages, but the exact sequence of events is difficult to grasp. It has been previously shown that related formyl-alkenyl complexes [Mo 2 Cp 2 (μ-PPh 2 )­{μ-κ 2 C,O :η 2 C,C -CRCRC­(O)­H}­(CO) 2 ] can be prepared through the thermal rearrangement of the corresponding alkyne complexes [Mo 2 Cp 2 (μ-η 2 :η 2 -C 2 R 2 )­(PPh 2 H)­(CO) 3 ] (R = H, CO 2 Me), , and similar rearrangements are suspected to be at the origin of the phosphinidene derivatives [Mo 2 Cp 2 {μ-κ 2 C,O :η 2 C,C -CHC­( t Bu)­C­(O)­H}­{μ-P­(CH 2 CMe 2 )­C 6 H 2 t Bu 2 }­(CO) 2 ] mentioned above . In these cases, an alkenyl ligand might be also involved at an intermediate stage, since the latter might be readily formed following from P–H bond cleavage at a PHR 2 ligand (to form the phosphanide ligand) and coupling of the resulting hydride ligand with the bridging alkyne.…”

Efficient Synthesis and Multisite Reactivity of a Phosphinidene-Bridged Mo–Re Complex. A Platform Combining Nucleophilic and Electrophilic Features

“…Compound 3 reacts with a variety of molecules under mild conditions displaying a remarkable multisite activity, related, in part, to the ambiphilic nature of the Mo–P–Re interaction discussed above (Scheme ). First we note that 3 rearranges into its phosphanyl hydride isomer [MoReCp­(μ-H)­{μ-P­(CH 2 CMe 2 )­C 6 H 2 t Bu 2 }­(CO) 6 ] ( 5 ; δ P 84.0 ppm and δ H −12.91 ppm) either photochemically (263 K) or even thermally (385 K) more easily than its Mo 2 analogue [Mo 2 Cp 2 (μ-PR*)­(CO) 4 ]. , This indicates the operation of some heterometallic effect at facilitating the corresponding C–H bond addition at the P atom and also resembles the reactivity of mononuclear electrophilic complexes…”

Optical Hall effect and gyrotropy of surface polaritons in Weyl semimetals

“…A number of recent studies have suggested that Weyl semimetals (WSMs) should have highly unusual optical response originated from unique topological properties of their bulk and surface electron states; see e.g. [1][2][3][4][5][6][7][8][9][10][11][12][13] and references therein. Their optical response can be used to provide detailed spectroscopic information about their electronic structure which could be difficult to obtain by any other means.…”