Chelate ring-opening of rhenium–diphosphine complexes by diazonium salts

Abstract

Treatment of [ReCl(CO)₅] with Ph₂PC(CH₂)PPh₂(vdpp) gave trans-[ReCl(CO)(vdpp-PP′)₂](1a); similar treatment with Ph₂PCH₂CH₂PPh₂(dppe) gave trans-[ReCl(CO)(dppe-pp′)₂](1b) but Ph₂PCH₂PPh₂(dppm) gave trans-[ReCl(CO)(dppm-pp′)₂](1c) as a minor product, the main product being mer, cis-[ReCl(CO)₂(dppm-PP′)(dppm-P)]. Treatment of [ReCl(CO)₅] with Ph₂PCHMePPh₂(mdppm) gave trans-[ReCl(CO)(mdppm-PP′)₂] as a mixture of two geometrical isomers; reduction of (1a) with sodium tetrahydroborate gave these same isomers but in different proportions. Treatment of (1a) with a solution of [4-FC₆H₄N₂][PF₆], even at –70 °C, caused immediate chelate ring-opening to give mer-[ReCl(CO)(N₂C₆H₄F-4)(vdpp-PP′)(vdpp-P)][PF₆], (5a), which was isolated in 90% yield; other diazonium salts, [4-MeC₆H₄N₂][BF₄], [4-MeOC₆H₄N₂][PF₆], or [2,6-Me₂-C₆H₃N₂][BF₄], similarly effected chelate ring-opening to give analogous complexes. In the case of mer-[ReCl(CO)(N₂C₆H₃Me₂-2,6)(vdpp-PP′)(vdpp-P)][BF₄] a mixture of two isomers was obtained; these were possibly due to restricted rotation around the Re–N₂ bond caused by the bulky aryl group. Treatment of trans-[ReCl(CO)(mdppm-PP′)₂](mixture of isomers) with [4-FC₆H₄N₂][PF₆] caused chelate ring-opening to give [ReCl(CO)(N₂C₆H₄F-4)(mdppm-PP′)(mdppm-P)][PF₆] as a mixture of two isomers The uncomplexed phosphorus of (5a) was methylated, on treatment with Me₃O·BF₄, to give [ReCl(CO)(N₂C₆H₄F-4)(vdpp-PP′){Ph₂PC(CH₂)PMePh₂}][BF₄][PF₆]. Treatment of (1b) with [4-FC₆H₄N₂][PF₆] caused oxidation to the Re^II complex trans-[ReCl(CO)(dppe-PP′)₂][PF₆] and no ring-opening; treatment of the dinitrogen complex trans-[ReCl(N₂)(dppm-PP′)₂] with [4- FC₆H₄N₂][PF₆] gave trans-[ReCl(N₂H₆-4)(dppm-PP′)₂][PF₆], also with no ring-opening. Phosphorus-31 and ¹H n.m.r. and i.r. data are given.