Reactions of Re2(CO)8 (L-L=dppm, dmpm) and Re2(CO)7(NCMe) with Alkynes

Article abstract of DOI:10.1021/ja00289a015

The photochemical reaction of Re2(CO)8<μ-(L-L)> (L-L=dppm, dmpm) with terminal alkynes, RC<*>CH (R=H, Ph), results in formation of (μ-H)Re2(CO)7<μ-(L-L)>(η¹-C<*>CRe2) (I), (μ-H)Re2(CO)6<μ-(L-L)>(μ-η¹,η²-C<*>CR) (II), Re2(CO)5(L-L)(μ-η¹,η²-C(R)=CH2(μ-η¹,η²-C<*>CR) (III), and Re2(CO)6<μ-(L-L)>(μ-η¹,η²-C(R)=CH2)(μ-η¹,η²-C<*>CR) (IV).The yield for each product depends on the reaction time and the bridging ligand.I is the first isolated example of bridging hydrido, ?-bonded alkynyl di- or polynuclear compounds directly formed from alkyne.In the reaction of II with acetylenes, coordination of dppm has been rearranged to form a chelate in III.The kinetic studies for the photochemical reactions of Re2(CO)8<μ-(L-L)> and the isolated compounds I and II (L-L=dppm; R=Ph) with phenylacetylene indicate that the consecutive reactions occur with loss of one carbonyl ligand in each step: Re2(CO)8(μ-dppm)->I->II->III.The reaction of Re2(CO)8<μ-(L-L)> with Me3NO in acetonitrile yields the acetonitrile-substituted complex Re2(CO)7<μ-(L-L)>(NCMe) (VI) wherein the acetonitrile ligand is located trans to phosphorus.The thermal reaction of VI with phenylacetylene at low temperature (40 deg C) yields I, in which the ?-bonded alkynyl ligand is cis to phosphorus.In the case of the reaction of Re2(CO)7(μ-dppm)(NCMe) with phenylacetylene, the isomer of I wherein ?-bonded alkynyl ligand is located trans to phosphorus is isolated as a minor product.I is transformed to II in a high-temperature thermal reaction reaction (110 deg C).The bridging alkynyl ligand of II undergoes a rapid fluxional process.The ΔG<*>_c value estimated from the coalescence temperature temperature in the 13C NMR spectra is 10.5 kcal/mol.The structures of (μ-H)Re2(CO)7(μ-dmpm)(η¹-C<*>CPh) (I_d) and Re2(CO)5(dppm)(μ-η¹,η²-CH=CH2)(μ-η¹,η²-C<*>CPh) (III_c) were determined by conventional crystallographic techniques with Mo Kα X-rays.The crystals of I_d belong to the monoclinic space group P2₁/c with a=12.594(1) Angstroem, b=11.075(1) Angstroem, c=18.461(3) Angstroem, β=105.88(1) deg, V=2476.8(9) Angstroem³, and z=4.The crystals of III_c belong to the orthorhombic space group Pbca with a=12.743(2) Angstroem, b=15.974(2) Angstroem, c=35.174(4) Angstroem, V=7160(2) Angstroem³, and Z=8.