Trinuclear and Tetranuclear Platinum−Iridium Cluster Complexes:  A Remarkable Metal for Metal Substitution Reaction

Abstract

The reaction of [Pt3(μ3-CO)(μ-dppm)3]2+, 1, dppm = Ph2PCH2PPh2, with [Ir(CO)4]- at low temperature gives [Pt3(μ3-CO)(μ-dppm)3{Ir(CO)4}]+, 2, and subsequent loss of CO leads to the butterfly complex [Pt3{Ir(CO)(μ-CO)2}(μ-CO)(μ-dppm)3]+, 3. Complex 3 reacts with L = P(OPh)3 to give [Pt3{IrL(μ-CO)2}(μ-CO)(μ-dppm)3]+, 4, which has been characterized by X-ray structure determination and has a butterfly structure with iridium at a wingtip position. Cluster 3 is thermally unstable and rearranges in solution to form the isomeric butterfly cluster cation [Pt2Ir{Pt(CO)(μ-CO)2}(CO)(μ-dppm)3]+, 5, in which the iridium atom now occupies a hinge position and whose formation involves phosphorus migration from platinum to iridium. Under CO, 5 eliminates one platinum atom to form the trimetallic complex [Pt2Ir(μ3-CO)(CO)(μ-dppm)3]+, 6. The overall reaction then involves displacement of a platinum atom from the 42-electron cluster cation 1 by {IrCO}- to give the 44-electron cation 6.

Complexes with Platinum−Iridium Bonds: Stepwise Formation of a PtIr2Cluster Complex

“…The resonance at δ −45.7 is therefore due to P c . These assignments are in accord with assignments of the 31 P NMR spectra of related clusters such as 1 and 2 , and the data are strongly indicative of the presence of a planar M 3 (μ-dppm) 3 unit in 3 . The 1 H NMR spectrum of the cluster 3 shows four broad resonances in a ratio of 2:2:1:1, assigned to the CH a H b P 2 protons of the dppm ligands.…”

“…Only P a shows a large coupling due to 1 J (PtP) = 3000 Hz, while the other three resonances show long-range coupling to 195 Pt with 2 J (PtP) = 24−92 Hz, indicating that one phosphorus atom is bound to platinum and the other three are bound to iridium. The coupling 3 J (P c P d ) = 44 Hz is much less than that expected if P d were in the PtIr 2 plane, since such values for a trans coupling across a metal−metal bond are typically >100 Hz . The 1 H NMR spectrum is also unusual in having one CH c H d P 2 proton at the unusual chemical shift of δ(H d ) = 7.0 (the normal range is δ 3−5); the resonance was obscured by phenyl group resonances but was identified in a COSY spectrum by its coupling to H c at δ 3.31.…”

“…There is interest in heteronuclear cluster complexes containing platinum and iridium, since they have the potential to act as models for bimetallic Pt−Ir-alumina catalysts, one of a group of bimetallic Pt−M catalysts including Pt−Ir, Pt−Re, and Pt−Sn on alumina which are used in petroleum refining . These bimetallic platinum−iridium catalysts have advantages over simple platinum catalysts on alumina in having both improved selectivity for dehydrocyclization rather than cracking of linear alkanes and longer active lifetimes …”

“…Platinum−iridium cluster complexes are relatively uncommon, and improved routes to stable platinum−iridium clusters are clearly needed in order for the reactivities to be studied. , Recently we described the formation of the cationic Pt 2 Ir cluster complex [Pt 2 Ir(CO) 2 (μ-dppm) 3 ] + ( 2 ) by reaction of the dicationic cluster complex [Pt 3 (μ 3 -CO)(μ-dppm) 3 ] 2+ ( 1 ) with [Ir(CO) 4 ] - , as shown in Scheme 1b. This reaction involves the formal substitution of Pt by {Ir(CO)} - , so that the 42-electron cluster 1 is converted to the 44-electron cluster 2 , thus allowing platinum and iridium centers to have 16- and 18-electron configurations, respectively.…”

Structural and Functional Evolution of Metallacrowns

“…[278][279][280]284,285,[287][288][289] In addition, Re(CO) 3 + groups have been attached to the Pt 3 core via three one-atom bridges between the Re and two ring Pt centers provided by two µ 3 -O and one µ 3 -S. 290,291 Re(CO) 3 + groups have also been attached to 12-MC Pt -3 complexes via two or three Re-Pt bonds and two µ 3 -one atom bridges provided by µ 3 -O, µ 3 -S, or µ-CO groups (Figure 27). An Ir(dppm) group 300 and an Ir(P(OC 6 H 5 ) 3 ) group 301 have been attached in a similar manner to a 12-MC Pt -3. A Ru- (CO) 2 complex has also been bound to a 12-MC Pt -3 complex by two Ru-Pt metal bonds and two µ-CO bridges.…”