Diphosphine Isomerization and C-H and P-C Bond Cleavage Reactivity in the Triosmium Cluster Os3(CO)10(bpcd): Kinetic and Isotope Data for Reversible Ortho Metalation and X-ray St
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- 作者：William H. Watson ; Guanmin Wu ; and Michael G. Richmond
- 刊名：Organometallics
- 出版年：2006
- 出版时间：February 13, 2006
- 年：2006
- 卷：25
- 期：4
- 页码：930 - 945
- 全文大小：414K
- 年卷期：v.25,no.4(February 13, 2006)
- ISSN：1520-6041
文摘
The coordination and reactivity of the diphosphine ligand 4,5-bis(diphenylphosphino)-4-cyclopentene-1,3-dione (bpcd) with Os3(CO)10(MeCN)2 (1) has been explored. The initial substitution product 1,2-Os3(CO)10(bpcd) (2b) undergoes a nondissociative, intramolecular isomerization to furnish the bpcd-chelated cluster 1,1-Os3(CO)10(bpcd) (2c) over the temperature range of 323-343 K. The isomerizationreaction is unaffected by trapping ligands, yielding the activation parameters 
H
= 25.0(0.7) kcal/moland S = -2(2) eu. Thermolysis of 2c in refluxing toluene gives the hydrido cluster HOs3(CO)9[
-(PPh2)C=C{PPh(C6H4)}C(O)CH2C(O)] (3) and the benzyne cluster HOs3(CO)8(3-C6H4)[2,
1-PPhC=C(PPh2)C(O)CH2C(O)] (4). Time-concentration profiles obtained from sealed-tube NMR experimentsstarting with either 2c or 3 suggest that both clusters are in equilibrium with the unsaturated cluster1,1-Os3(CO)9(bpcd) and that the latter cluster serves as the precursor to the benzyne-substituted cluster 4.The product composition in these reactions is extremely sensitive to CO, with the putative cluster 1,1-Os3(CO)9(bpcd) being effectively scavenged by CO to regenerate 2c. Photolysis of cluster 2c using near-UV light affords 3 as the sole product. These new clusters have been fully characterized in solution byIR and NMR spectroscopy, and the molecular structures of clusters 2b,c, and 4 have been determined byX-ray crystallography. Reversible C-H bond formation in cluster 3 is demonstrated by ligand trappingstudies to give 1,1-Os3(CO)9L(bpcd) (where L = CO, phosphine) via the unsaturated intermediate 1,1-Os3(CO)9(bpcd). The kinetics for reductive coupling in HOs3(CO)9[-(PPh2)C=C{PPh(C6H4)}C(O)CH2C(O)] and DOs3(CO)9[-(PPh2-d10)C=C{P(Ph-d5)(C6D4)}C(O)CH2C(O)] in the presence of PPh3 give riseto a kH/kD value of 0.88, a value that supports the existence of a preequilibrium involving the hydride(deuteride) cluster and a transient arene-bound Os3 species that precedes the rate-limiting formation of 1,1-Os3(CO)9(bpcd). Strong proof for the proposed hydride (deuteride)/arene preequilibrium has been obtainedfrom photochemical studies employing the isotopically labeled cluster 1,1-Os3(CO)10(bpcd-d4,ortho), whosebpcd phenyl groups each contain one ortho hydrogen and deuterium atom. Generation of 1,1-Os3(CO)9-(bpcd-d4,ortho) at 0 
C gives rise to a 55:45 mixture of the corresponding hydride and deuteride clusters, re-spectively, from which a normal KIE of 1.22 is computed for oxidative coupling of the C-H(D) bond inthe ortho metalation step. Photolysis of 1,1-Os3(CO)10(bpcd-d4,ortho) at elevated temperature and thermolysisof the low-temperature photolysis hydride/deuteride mixture afford an equilibrium mixture of hydride(67%) and deuteride (33%), yielding a Keq value of 0.49, which in conjunction with the kH/kD ratio fromthe C-H(D) ortho-metalation step allows us to establish a kH/kD value of 0.60 for the reductive couplingfrom the participant hydride/deuteride clusters. These data, which represent the first isotope study on orthometalation in a polynuclear system, are discussed relative to published work on benzene activation at mono-nuclear rhodium systems. UV-vis kinetic data on the transformation 3 
4 provide activation parametersconsistent with the rate-limiting formation of the unsaturated cluster 1,1-Os3(CO)9(bpcd), preceding theirreversible P-C cleavage manifold. The ortho metalation of the bpcd ligand in 3 and formation of thebenzyne moiety 4 are discussed relative to ligand degradation reactions in this genre of cluster.
H = 25.0(0.7) kcal/moland S = -2(2) eu. Thermolysis of 2c in refluxing toluene gives the hydrido cluster HOs3(CO)9[-(PPh2)C=C{PPh(C6H4)}C(O)CH2C(O)] (3) and the benzyne cluster HOs3(CO)8(3-C6H4)[2,1-PPhC=C(PPh2)C(O)CH2C(O)] (4). Time-concentration profiles obtained from sealed-tube NMR experimentsstarting with either 2c or 3 suggest that both clusters are in equilibrium with the unsaturated cluster1,1-Os3(CO)9(bpcd) and that the latter cluster serves as the precursor to the benzyne-substituted cluster 4.The product composition in these reactions is extremely sensitive to CO, with the putative cluster 1,1-Os3(CO)9(bpcd) being effectively scavenged by CO to regenerate 2c. Photolysis of cluster 2c using near-UV light affords 3 as the sole product. These new clusters have been fully characterized in solution byIR and NMR spectroscopy, and the molecular structures of clusters 2b,c, and 4 have been determined byX-ray crystallography. Reversible C-H bond formation in cluster 3 is demonstrated by ligand trappingstudies to give 1,1-Os3(CO)9L(bpcd) (where L = CO, phosphine) via the unsaturated intermediate 1,1-Os3(CO)9(bpcd). The kinetics for reductive coupling in HOs3(CO)9[-(PPh2)C=C{PPh(C6H4)}C(O)CH2C(O)] and DOs3(CO)9[-(PPh2-d10)C=C{P(Ph-d5)(C6D4)}C(O)CH2C(O)] in the presence of PPh3 give riseto a kH/kD value of 0.88, a value that supports the existence of a preequilibrium involving the hydride(deuteride) cluster and a transient arene-bound Os3 species that precedes the rate-limiting formation of 1,1-Os3(CO)9(bpcd). Strong proof for the proposed hydride (deuteride)/arene preequilibrium has been obtainedfrom photochemical studies employing the isotopically labeled cluster 1,1-Os3(CO)10(bpcd-d4,ortho), whosebpcd phenyl groups each contain one ortho hydrogen and deuterium atom. Generation of 1,1-Os3(CO)9-(bpcd-d4,ortho) at 0 C gives rise to a 55:45 mixture of the corresponding hydride and deuteride clusters, re-spectively, from which a normal KIE of 1.22 is computed for oxidative coupling of the C-H(D) bond inthe ortho metalation step. Photolysis of 1,1-Os3(CO)10(bpcd-d4,ortho) at elevated temperature and thermolysisof the low-temperature photolysis hydride/deuteride mixture afford an equilibrium mixture of hydride(67%) and deuteride (33%), yielding a Keq value of 0.49, which in conjunction with the kH/kD ratio fromthe C-H(D) ortho-metalation step allows us to establish a kH/kD value of 0.60 for the reductive couplingfrom the participant hydride/deuteride clusters. These data, which represent the first isotope study on orthometalation in a polynuclear system, are discussed relative to published work on benzene activation at mono-nuclear rhodium systems. UV-vis kinetic data on the transformation 3 4 provide activation parametersconsistent with the rate-limiting formation of the unsaturated cluster 1,1-Os3(CO)9(bpcd), preceding theirreversible P-C cleavage manifold. The ortho metalation of the bpcd ligand in 3 and formation of thebenzyne moiety 4 are discussed relative to ligand degradation reactions in this genre of cluster.