Reversible Isomerization of a Diphosphine Ligand about a Triosmium Cluster:  Synthesis, Kinetics, and X-ray Structures for the Bridging and Chelating Isomers of Os₃(CO)₁₀[(Z)-Ph₂PCHCHPPh₂]

Abstract

Substitution of the MeCN ligands in the activated cluster Os3(CO)10(MeCN)2 (1) by the unsaturated diphosphine ligand (Z)-Ph2PCHCHPPh2 proceeds rapidly at room temperature to furnish the ligand-bridged cluster 1,2-Os3(CO)10[(Z)-Ph2PCHCHPPh2] (2b). Heating 2b leads to the formation of the thermodynamically more stable chelating isomer 1,1-Os3(CO)10[(Z)-Ph2PCHCHPPh2] (2c). The molecular structure of each isomer of 2 has been crystallographically determined, and the 31P NMR data have been recorded. The kinetics for the ligand isomerization have been investigated by UV−vis and 31P NMR spectroscopy in toluene solution over the temperature range of 358−383 K. The reversible nature of the diphosphine isomerization is confirmed by 31P NMR measurements, and reported within are the forward (k 1) and reverse (k - 1) first-order rate constants for the bridge-to-chelate rearrangement. On the basis of the activation parameters and lack of CO inhibition on the reaction rate, a nondissociative, intramolecular mechanism involving the migration of one P group from an adjacent osmium center to the other P-substituted osmium center via a μ2-bridged phosphine species is presented.

Pincer ligand coordination at a triosmium cluster: X-ray structures of 1,2-Os3(CO)10[4,6-bis(diphenylphosphinomethyl)-m-xylene] and 1,2-Os3(CO)10[1-diphenylphosphino-1-{(2,4-dimethyl-5-diphenylphosphinomethyl)phenyl}-propan-2-ol]

“…These data confirm that cyclometalation of the dppx ligand has not occurred. The high-field 31 P singlet recorded at d À0.76 for 2 is in accord with the proposed structure and the NMR data reported by us for other diphosphinebridged Os 3 clusters [15]. The molecular structure for 2 is shown in Fig.…”

Fluorous triosmium clusters. Preparation, properties, and reactivity of Os3(CO)11{P(CH2CH2(CF2)5CF3)3} and Os3(CO)10{P(CH2CH2(CF2)5CF3)3}2. Crystal structure of Os3(CO)9(PPh3)2{P(CH2CH2(CF2)5CF3)3}. Ring opening metathesis polymerization of norbornene by (μ-H)2Os3(CO)9{P(C6H4-4-CH2CH2(CF2)7CF3)3}

“…This conclusion supports earlier positions of isomerization based on limited turnstile rotations at those osmium atoms possessing phosphine or phosphite ligands [32aec]. However, there has been a recent report regarding the isomerization of Os 3 (CO) 10 unsaturated derivative of diphenylphosphinoethane, (Z)-Ph 2 PCH] CHPPh 2 [33]. This cluster exhibited reversible diphosphine isomerization from a bridged configuration, along one edge of the osmium triangle, to a chelated configuration.…”

“…for C 33 In a 3-neck 50 mL round bottom flask with condenser, gas inlet, thermometer adapter, and magnetic stir bar, 40.0 mg, 0.0205 mmol, of 1 were dissolved in 15.0 mL of perfluoromethyldecalin, and the yellow solution was sparged with H 2 for 30 min. The flask was placed in an oil bath and maintained under an H 2 atmosphere at an internal temperature of 102 C for 135 min.…”

New osmium cluster compounds containing the heterocyclic ligand 2,3-bis-(diphenylphosphino)quinoxaline (dppq): Ligand isomerization and crystal structures of dppq, the isomeric clusters Os3(CO)10(dppq), and HOs3(CO)9[μ-2,3-PhP(η1-C6H4)(Ph2P)quinoxaline]

“…The reactivity of a wide variety of ligands at the activated cluster 1,2-Os 3 (CO) 10 (MeCN) 2 (1) has been intensely explored over the years. Of the many different classes of ligands examined, diphosphine ligands have received extensive attention.…”

“…The reaction between 1 and the diphosphine ligands (Z)-Ph 2 PCH ¼ CHPPh 2 (dppen) [2], 4,5-bis(diphenylphosphino)-4-cyclopentene-1,3-dione (bpcd) [3], 2,3-bis(diphenylphosphino)-N-p-tolylmaleimide (bmi) [4], 2-(ferrocenylidene)-4,5-bis (diphenylphosphino)-4-cyclopentene-1,3-dione (fbpcd) [5], 3,4-bis(diphenylphosphino)-5-methoxy-2(5H)-furanone (bmf), and 1,2-bis(diphenylphosphino)benzene (dppbz) has been explored by us, as part of our interest in the coordinative flexibility and ligand activation of these and related ligands at polynuclear clusters. The structures of these particular diphosphine ligands are depicted in Scheme 1.…”