Chemistry of Diruthenium and Dirhodium Analogues of Pentaborane(9): Synthesis and Characterization of Metal N,S‐Heterocyclic Carbene and B‐Agostic Complexes

Abstract

Building upon our earlier results on the synthesis of electron-precise transition-metal-boron complexes, we continue to investigate the reactivity of pentaborane(9) and tetraborane(10) analogues of ruthenium and rhodium towards thiazolyl and oxazolyl ligands. Thus, mild thermolysis of nido-[(Cp*RuH)2B3H7] (1) with 2-mercaptobenzothiazole (2-mbtz) and 2-mercaptobenzoxazole (2-mboz) led to the isolation of Cp*-based (Cp* = η(5)-C5Me5) borate complexes 5 a,b [Cp*RuBH3L] (5 a: L = C7H4NS2; 5 b: L = C7H4NOS)) and agostic complexes 7 a,b [Cp*RuBH2(L)2], (7 a: L = C7H4NS2; 7 b: L = C7H4NOS). In a similar fashion, a rhodium analogue of pentaborane(9), nido-[(Cp*Rh)2B3H7] (2) yielded rhodaboratrane [Cp*RhBH(L)2], 10 (L = C7H4NS2). Interestingly, when the reaction was performed with an excess of 2-mbtz, it led to the formation of the first structurally characterized N,S-heterocyclic rhodium-carbene complex [(Cp*Rh)(L2)(1-benzothiazol-2-ylidene)] (11) (L = C7H4NS2). Furthermore, to evaluate the scope of this new route, we extended this chemistry towards the diruthenium analogue of tetraborane(10), arachno-[(Cp*RuCO)2B2H6] (3), in which the metal center possesses different ancillary ligands.

An Efficient Method for the Synthesis of Boratrane Complexes of Late Transition Metals

“…The structures of compounds 6 and 7 are similar to that of 5 . Although the Ir→B bond distance of 2.136(13) Å is comparable to those in reported iridaboratranes,– the Rh→B distance of 2.12(3) Å is somewhat shorter than those in reported boratrane complexes of rhodium (see Table ) …”

“…Thus, we anticipated that [(η 6 ‐ p ‐cymene)RuCl 2 ] 2 could be a potential precursor for the generation of p ‐cymene‐based ruthenaboratrane complexes. As a result, in an attempt to synthesize the Ru analogue of the rhodaboratrane complex [Cp*RhBH(L) 2 ] (L=C 7 H 4 NS 2 ),, we carried out reactions of [(η 6 ‐ p ‐cymene)RuCl 2 ] 2 with both [NaBt] (Bt=dihydrobis(2‐mercaptobenzothiazolyl)borate) and [NaBo] (Bo=dihydrobis(2‐mercaptobenzoxazolyl)borate). Unfortunately, all of our attempts to generate ruthenaboratrane complexes were unsuccessful.…”

“…In an effort to find efficient methods for the preparation of such complexes, we used different synthetic precursors. One of the useful precursors identified was [Cp*MCl 2 ] 2 (M=Rh or Ir), which enabled us to isolate several metallaboratrane complexes in good yields ,. As a result, in an extension of our previous work, we explored this chemistry with Group 8 metals.…”

Adding to the Family of Copper Complexes Featuring Borohydride Ligands Based on 2-Mercaptopyridyl Units

“…It was this greater flexibility within the ligand structure that opened up the potential for activation at the boron bridgehead and formation of metal-borane (metallaboratrane) complexes [17][18][19][20][24][25][26][27], giving rise to reactivity not observed in the analogous polypyrazolylborate ligands [10][11][12][13][14][15][16]. Over the following twenty years since the first report of hydride migration from the boron center of a scorpionate ligand, a number of research groups have focused on new, more flexible borohydride ligands containing a range of supporting units based on nitrogen [28][29][30][31] and other sulfur heterocycles [32][33][34][35][36][37][38][39][40][41][42][43][44][45][46]. As part of our research, we have focused on providing new derivative ligand systems.…”

“…The first of the more flexible scorpionate ligands was [Tm] − [hydrotris(methylimidazolyl)borate] (Figure 1; middle) [23]. This new ligand had two major Over the following twenty years since the first report of hydride migration from the boron center of a scorpionate ligand, a number of research groups have focused on new, more flexible borohydride ligands containing a range of supporting units based on nitrogen [28][29][30][31] and other sulfur heterocycles [32][33][34][35][36][37][38][39][40][41][42][43][44][45][46]. As part of our research, we have focused on providing new derivative ligand systems.…”