Early−Late Heterotetranuclear Complexes (TiRh₃) with Bridging Sulfido Ligands:  Ligand Replacement Reactions and Catalytic Activity in Hydroformylation of Olefins

Abstract

The tetranuclear early−late heterobimetallic (TiRh3) complexes [CpTi(μ3-S)3{Rh(diolef)}3] (diolef = tfbb (1), cod (2)) in the presence of P-donor ligands are active precursors in the hydroformylation of hex-1-ene and styrene under mild conditions of pressure and temperature. A 96% conversion to aldehydes and 77% regioselectivity for the linear aldehyde is obtained in the hydroformylation of hex-1-ene using PPh3 (P/Rh = 2−4) as the P-donor ligand at 5 bar and 353 K. Hydroformylation of styrene under similar conditions (10 bar) gives 70% conversion and 88% regioselectivity in favor of 2-phenylpropanal. The reaction of [CpTi(μ3-S)3{Rh(CO)2}3] (3) with monodentate P-donor ligands results in the selective synthesis of the C 3 isomer of the complexes [CpTi(μ3-S)3Rh3(CO)3(PR3)3]. The compound [CpTi(μ3-S)3Rh3(CO)3(PPh3)3] (5) reacts reversibly with carbon monoxide to give the 62-electron valence clusters [CpTi(μ3-S)3Rh3(μ-CO)(CO)4(PPh3)2] (4b) and [CpTi(μ3-S)3Rh3(μ-CO)(CO)3(PPh3)3] (4c), which are in equilibrium. High-pressure NMR spectroscopic studies have shown that both clusters are also formed under hydroformylation conditions. A multinuclear NMR spectroscopic investigation of the replacement reactions shows that [CpTi(μ3-S)3Rh3(CO)5(PPh3)] (4a), 4b, and 4c are intermediary species in the replacement reactions leading to 5, the decarbonylation of 4c being the key step for the observed stereoselectivity. The reaction of 3 with diphosphines gives the complexes [CpTi(μ3-S)3Rh3(μ-P−P)(CO)4] (P−P = 1,2-bis(diphenylphosphine)ethane (dppe); 1,3-bis(diphenylphosphine)propane, (dppp)), [CpTi(μ3-S)3Rh3(CO)4(η2-(R)-BINAP)], and [CpTi(μ3-S)3Rh3(μ-dppe)(CO)2(η2-dppe)], in which the heterotetranuclear metal framework is maintained.

Homogeneous Catalysis by Organometallic Polynuclear Clusters

“…However, the role of Zr is in large suggested to ensure that the Rh-centres remain vicinal thereby warranting a cooperativity between the two Rh-centers. P. 41 of 52 [155]. Probing 123 with monodentate phosphine and phosphites, the authors were able to ascertain the active catalyst to exist in an equilibrium between a bis-(123a) and a tris ligated (123b and 123c) compound type, as shown in Scheme 35.…”

Reactivity of [TiM2] (M = Rh, Ir) and [TiIr3] early-late heterobimetallic sulfido-bridged clusters

“…2 [CpTi(µ 3 -S) 3 Ir 3 (µ 2 -CO)(CO) 3 (PMe 3 ) 3 ] (10) reacts with alkynes at the triiridium metallic triangle. The reactions with activated alkynes, such as dimethyl acetylenedicarboxylate (or diethyl acetylenedicarboxylate) afford clusters [CpTi(µ 3 -S) 3 Ir 3 (µ 2 -η 1 -RO 2 CC=CCO 2 R){C(O)RO 2 CC=CCO 2 R}(CO) 3 (PMe 3 ) 3 ] (R = Me (11), Et (12)), which incorporate two molecules of alkyne.…”

“…6,7 In fact, we have reported the usefulness of the compounds [Cp 2 Ti(SH) 2 ] and [Cp tt 2 Zr(SH) 2 ] (Cp tt = η 5 -1,3-di-tert-butylcyclopentadienyl) as precursors for the synthesis of d 0 -d 8 sulfido-bridged ELHB complexes or clusters through additive deprotonation reactions with mono-and dinuclear d 8 rhodium and iridium compounds having protonable ligands. 8 This strategy has led to the preparation of the expected heterotrinuclear clusters with a triangular [ZrM 2 ] (M = Rh, Ir) core capped with two µ 3 -sulfido ligands, 9 but also unexpected clusters of composition [TiM 3 ] (M = Rh, Ir), with an incomplete cubane structure, 10 and [Ti 2 Rh 4 ] oxo-sulfido clusters, with an incomplete double-fused cubane structure. 11 Noteworthy, the carbonyl iridium complex [Cp tt 2 Zr(µ 3 -S) 2 {Ir(CO) 2 } 2 ] is a precursor for the synthesis of early-late heterotrimetallic (ELHT) clusters with [ZrIrM] (M = Rh, Pd, Au) metal cores by metal exchange reactions.…”

From atoms to biomolecules: a fruitful perspective

“…Transition metal containing molecules have a potential astrophysical importance [109] and present an interest in catalysis and organometallic chemistry [24]. Numerous diatomic molecules MX made of a transition metal atom M and a second or third row atom X have been studied in laboratory using Fourier transform emission spectroscopy.…”