Pentamethylcyclopentadienyl-rhodium and -iridium complexes. Part 19. Preparation and reactions of azido-, cyanato-, thiocyanato-, nitrito-, and nitrato-rhodium complexes

Abstract

Metathesis reactions of [Rh₂(C₅Me₅)₂Cl₄](1) with NaX give [Rh₂(C₅Me₅)₂X₄][X = N₃(2), NCO (9), or SCN (14)]. The dimeric azido-complex (2) is cleaved by unidentate ligands [L = PPh₃, P(OR)₃, CNR, py, etc.] to give monomeric adducts [Rh(C₅Me₅)(N₃)₂L](3); 1,10-phenanthroline gives [Rh(C₅Me₅)(N₃)(phen)][N₃] and 2,2′-bipyridyl gives [Rh(C₅Me₅)(N₃)(bipy)][Rh(C₅Me₅)(N₃)₃]. The azido-complexes undergo carbonylation: (2) gives first [Rh₂(C₅Me₅)₂(NCO)₃(N₃)](containing a bridging azide and a bridging cyanate ligand) and then (9), which is cleaved by PPh₃ to give [Rh(C₅Me₅)(NCO)₂(PPh₃)](12). Complex (12) is also obtained by carbonylation of [Rh(C₅Me₅)(N₃)₂(PPh₃)](3a). Equilibrium constants have been determined for the reactions of (2) and (9) with pyridine to give [Rh(C₅Me₅)X₂(py)](X = N₃ or NCO). Complex (3a) reacts with CS₂ to give (14)via[{Rh(C₅Me₅)(N₃CS₂)₂}_n]; [Rh(C₅Me₅)(SCN)₂(PPh₃)] is obtained by reaction of (3a) with Na[NCS] or by reaction of (14) with PPh₃. Complex (2) reacts with hexafluorobut-2-yne to give first [Rh₂(C₅Me₅)₂{N₃C₂(CF₃)₂}₂(N₃)₂](containing two bridging azide ligands) and then [Rh₂(C₅Me₅)₂[N₃C₂(CF₃)₂]₃(N₃)](18, containing one bridging azide and one bridging and two terminally bonded triazolate ligands). Similarly, (2) reacts with CF₃CN to give [Rh₂(C₅Me₅)₂(N₄CCF₃)₃(N₃)](containing one bridging azide and one bridging and two terminally bonded tetrazolate ligands). These results show that terminal azide ligands are very much more reactive than bridging ones. Reaction of complex (1) with sodium (or potassium) nitrite gives M[Rh(C₅Me₅)(NO₂)₃] which, with PPh₃, gives [Rh(C₅Me₅)(NO₂)₂(PPh₃)]; this complex could also be obtained from [Rh(C₅Me₅)Cl₂(PPh₃)] and Ag[NO₂]. Reaction of complex (2) with N₂O₄ gives monomeric [Rh(C₅Me₅)(NO₃)₂](24), but reaction of (1) with Ag[NO₃] gives the ionic isomer [Rh₂(C₅Me₅)₂(NO₃)₃][NO₃](25). Complex (24) gives [Rh(C₅Me₅)(NO₃)₂(PPh₃)] with PPh₃, but (25) does not react. Structures for these complexes are proposed on the basis of i.r. and ¹H, ¹³C, ¹⁹F, and ³¹P n.m.r. spectroscopic studies. The structure of complex (18) has been confirmed by a single-crystal X-ray determination which also showed that both rhodiums are bonded to N(1) of the bridging azide ligand.