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.