Xantphos-Type Complexes of Group 9: Rhodium versus Iridium

Treatment of the dimer [Rh­(μ-Cl)­(C8H14)2]2 (1a)
with 9,9-dimethyl-4,5-bis­(diisopropylphosphino)­xanthene [xant­(PiPr2)2] leads to the d8 square-planar
complex RhCl­{xant­(PiPr2)2} (2), whereas reaction of the iridium counterpart [Ir­(μ-Cl)­(C8H14)2]2 (1b)
gives the d6 octahedral compound IrHCl­{xant­(PiPr2)­[iPrPCH­(Me)­CH2]}
(3) as a result of the intramolecular C–H bond
activation of one of the isopropyl substituents of the phosphine.
Stirring 2 and 3 in 0.5 N KOH solutions
of 2-propanol gives rise to the formation of hydrides RhH­{xant­(PiPr2)2} (4) and IrH3{xant­(PiPr2)2} (5), respectively. In n-octane at 60 °C, complex 2 is stable. However, compound 3 activates the
alkane to give the cis-dihydride IrH2Cl­{xant­(PiPr2)2} (6) and a mixture
of 3- and 4-octene. Complex 6 can be also obtained by
the reaction of 3 with H2. Under the same
conditions, 2 affords the rhodium analogue RhH2Cl­{xant­(PiPr2)2} (7). Compounds 2–4 react with triflic
acid (HOTf) to give RhHCl­(OTf)­{xant­(PiPr2)2} (8), IrHCl­(OTf)­{xant­(PiPr2)2} (9), and RhH2(OTf)­{xant­(PiPr2)2} (10), respectively.
The related iridium derivative IrH2(OTf)­{xant­(PiPr2)2} (11) has also been prepared
by the reaction of 6 with Tl­(OTf). Complexes 2, 6, and 9 have been characterized by X-ray
diffraction analysis. The {xant­(PiPr2)2}­M skeleton is T-shaped with the metal center situated in the common
vertex.