C-C coupling of alkynes to the CH 2 group in a 1-phosphonioethenyl ligand in a zwitterionic dirhenium carbonyl complex

Reactions of the zwitterionic dirhenium complex Re2 (CO)8[mu-eta 2-1-C(CH2)(PMePh2)], 3 with the terminal alkynes, HC=C(OEt) and HC =CPh, have yielded two new isomeric ethoxy-substituted dirhenium complexes, Re2(CO)7[11-eta 3-C(H)C(OCH2CH3)CH2C(PMePh2)], 5 and Re2(CO)7[11-eta 3-C(OCH2CH3)C(H)CH2C(PMePh2)], 6 and one phenyl-substituted dirhenium complex Re2(CO)7[11-eta 3-C(H)CPhCH2C(PMePh2)], 7 , respectively, with each containing a bridging, substituted 1-phosphonio-3,4-butenyl ligand formed by loss of CO and the addition and coupling of one alkyne to the CH2 group of the 1-phosphonioethenyl ligand in 3 . The bridging 1-phosphonio-3,4-butenyl ligand in compound 6 exhibits a dynamical flip-flop exchange for the phosphonio-3,4-butenyl ligand between the two rhenium atoms that leads to an averaging of the inequivalent protons on its methylene group that is rapid on the NMR timescale. When heated to 70 oC, compound 5 was converted to two new compounds: Re2(CO)6(11-H)[11-eta 4-C(H)C(OCH2CH3)CHC(PMePh2)], 8 , by loss of a CO ligand and a CH activation at the CH2 group in its C(H)C(OCH2CH3)CH2C( +PMePh2) ligand and an isomer Re2(CO)6(PMePh2)[11-eta 4-C(H)C(OCH2CH3)CHCH], 9 . Compound 9 was also obtained from 8 by heating to 80 degrees C for 5 days by shifting the PMePh2 group from its phosphonium carbon atom in 8 to one of the rhenium atoms to become a PMePh2 ligand in 9 and then shifting the hydrido ligand back to the same carbon atom to form a bridging eta 4-2-ethoxybutadiendiyl, [C(H)C(OCH2CH3)CHCH], ligand. All new products were characterized structurally by single-crystal X-ray diffraction analyses.(c) 2022 Elsevier B.V. All rights reserved.

Automated summary

The reactions of a dirhenium complex with terminal alkynes resulted in the formation of new ethoxy-substituted dirhenium complexes and a phenyl-substituted dirhenium complex. The products were characterized by the formation of bridging phosphonio-3,4-butenyl ligands through CO loss and alkyne addition and coupling reactions. The dynamic flip-flop exchange of the bridging ligand was observed in one of the compounds. Furthermore, additional compounds were obtained by heating reactions.