Rhodium and iridium olefin complexes with bulky cyclopentadienyl and hydrotris(pyrazolyl)borate ligands

The synthesis of a series of rhodium and iridium complexes bearing bulky cyclopentadienyl or hydro(trispyrazolyl)borate ligands is described. The rhodium cyclopentadienyl and hydrotris(pyrazolyl)borate diene compounds, [(η5-C5Me4But)Rh(η4-2,3-MeRC4H4] (R = H, 1; Me, 2) and TpMsRh(η4-2,3-MeRC4H4) (R = H, 3; Me, 4; TpMs is hydrotris(3-mesitylpyrazol-1-yl)borate), respectively, have been prepared from the corresponding Rh(I) diene precursors and Zn(C5Me4But)2 (for 1 and 2), or TlTpMs (for 3 and 4), as effective C5Me4But or TpMs transfer reagents. In contrast with these results, attempts to obtain a bis(ethylene) derivative of the TptolIr(I) unit (Tptol stands for hydrotris(3-p-tolylpyrazol-1-yl)borate) have provided instead the Ir(III) complex [(κ4-N,N′,N″,C-Tptol)-Ir(C2H5)(C2H4)] (5), whose formation requires C–H bond activation of a molecule of ethylene and of one of the Tptolp-tolyl substituents. In refluxing toluene 5 experiences metalation of a second p-tolyl substituent to give [(κ5-N,N′,N″,C,C′-Tptol)-Ir(C2H4)] (6), which features unusual κ5-Tptol coordination. The latter compound reacts with carbon monoxide to yield the corresponding carbonyl, 7.

The bulky C5Me4But and TpMs ligands give rise to stable complexes of Rh(η4-diene) units, whereas the putative [TptolIr(C2H4)2] converts spontaneously in the Ir(III) complex [Tptol′Ir(C2H5)(C2H4)] (5), that contains a monometalated κ4-N,N′,N″,C-Tptol ligand. Under more drastic thermal conditions (115 °C) 5 experiences a second metalation to yield complex [(κ5-N,N′,N″,C,C′-Tptol)Ir(C2H4)] (6), that exhibis κ5 coordination of the tris(pyrazolyl)borate ligand.Figure optionsDownload as PowerPoint slide