10.1021/om050839t.s006
William H. Watson
William H.
Watson
Guanmin Wu
Guanmin
Wu
Michael G. Richmond
Michael G.
Richmond
Diphosphine Isomerization and C−H and P−C Bond Cleavage
Reactivity in the Triosmium Cluster Os<sub>3</sub>(CO)<sub>10</sub>(bpcd): Kinetic and
Isotope Data for Reversible Ortho Metalation and X-ray Structures
of the Bridging and Chelating Isomers of Os<sub>3</sub>(CO)<sub>10</sub>(bpcd) and the
Benzyne-Substituted Cluster
HOs<sub>3</sub>(CO)<sub>8</sub>(μ<sub>3</sub>-C<sub>6</sub>H<sub>4</sub>)[μ<sub>2</sub>,η<sup>1</sup>-PPhCC(PPh<sub>2</sub>)C(O)CH<sub>2</sub>C(O)]<sup>†</sup>
American Chemical Society
2006
2 c
benzyne moiety 4
cluster 2 c
KIE
K eq value
Os 3
ortho metalation
UV
ligand degradation reactions
bpcd phenyl groups
ortho metalation step
Triosmium Cluster Os 3
CO
Reversible Ortho Metalation
clusters 2 b
NMR
DO
benzyne cluster HOs 3
hydrido cluster HOs 3
IR
2006-02-13 00:00:00
Journal contribution
https://acs.figshare.com/articles/journal_contribution/Diphosphine_Isomerization_and_C_H_and_P_C_Bond_Cleavage_Reactivity_in_the_Triosmium_Cluster_Os_sub_3_sub_CO_sub_10_sub_bpcd_Kinetic_and_Isotope_Data_for_Reversible_Ortho_Metalation_and_X_ray_Structures_of_the_Bridging_and_Chelating_Isomers_of_Os_sub_3_sub/3238744
The coordination and reactivity of the diphosphine ligand 4,5-bis(diphenylphosphino)-4-cyclopentene-1,3-dione (bpcd) with Os<sub>3</sub>(CO)<sub>10</sub>(MeCN)<sub>2</sub> (<b>1</b>) has been explored. The initial substitution product 1,2-Os<sub>3</sub>(CO)<sub>10</sub>(bpcd) (<b>2b</b>) undergoes a nondissociative, intramolecular isomerization to furnish the bpcd-chelated cluster 1,1-Os<sub>3</sub>(CO)<sub>10</sub>(bpcd) (<b>2c</b>) over the temperature range of 323−343 K. The isomerization
reaction is unaffected by trapping ligands, yielding the activation parameters Δ<i>H</i><sup>⧧</sup> = 25.0(0.7) kcal/mol
and Δ<i>S</i><sup>⧧</sup> = −2(2) eu. Thermolysis of <b>2c</b> in refluxing toluene gives the hydrido cluster HOs<sub>3</sub>(CO)<sub>9</sub>[μ-(PPh<sub>2</sub>)CC{PPh(C<sub>6</sub>H<sub>4</sub>)}C(O)CH<sub>2</sub>C(O)] (<b>3</b>) and the benzyne cluster HOs<sub>3</sub>(CO)<sub>8</sub>(μ<sub>3</sub>-C<sub>6</sub>H<sub>4</sub>)[μ<sub>2</sub>,η<sup>1</sup>-PPhCC(PPh<sub>2</sub>)C(O)CH<sub>2</sub>C(O)] (<b>4</b>). Time−concentration profiles obtained from sealed-tube NMR experiments
starting with either <b>2c</b> or <b>3</b> suggest that both clusters are in equilibrium with the unsaturated cluster
1,1-Os<sub>3</sub>(CO)<sub>9</sub>(bpcd) and that the latter cluster serves as the precursor to the benzyne-substituted cluster <b>4</b>.
The product composition in these reactions is extremely sensitive to CO, with the putative cluster 1,1-Os<sub>3</sub>(CO)<sub>9</sub>(bpcd) being effectively scavenged by CO to regenerate <b>2c</b>. Photolysis of cluster <b>2c</b> using near-UV light affords <b>3</b> as the sole product. These new clusters have been fully characterized in solution by
IR and NMR spectroscopy, and the molecular structures of clusters <b>2b</b>,<b>c</b>, and <b>4</b> have been determined by
X-ray crystallography. Reversible C−H bond formation in cluster <b>3</b> is demonstrated by ligand trapping
studies to give 1,1-Os<sub>3</sub>(CO)<sub>9</sub>L(bpcd) (where L = CO, phosphine) via the unsaturated intermediate 1,1-Os<sub>3</sub>(CO)<sub>9</sub>(bpcd). The kinetics for reductive coupling in HOs<sub>3</sub>(CO)<sub>9</sub>[μ-(PPh<sub>2</sub>)CC{PPh(C<sub>6</sub>H<sub>4</sub>)}C(O)CH<sub>2</sub>C(O)] and DOs<sub>3</sub>(CO)<sub>9</sub>[μ-(PPh<sub>2</sub>-<i>d</i><sub>10</sub>)CC{P(Ph-<i>d</i><sub>5</sub>)(C<sub>6</sub>D<sub>4</sub>)}C(O)CH<sub>2</sub>C(O)] in the presence of PPh<sub>3</sub> give rise
to a <i>k</i><sub>H</sub>/<i>k</i><sub>D</sub> value of 0.88, a value that supports the existence of a preequilibrium involving the hydride
(deuteride) cluster and a transient arene-bound Os<sub>3</sub> species that precedes the rate-limiting formation of 1,1-
Os<sub>3</sub>(CO)<sub>9</sub>(bpcd). Strong proof for the proposed hydride (deuteride)/arene preequilibrium has been obtained
from photochemical studies employing the isotopically labeled cluster 1,1-Os<sub>3</sub>(CO)<sub>10</sub>(bpcd-<i>d</i><sub>4,</sub><i><sub>ortho</sub></i>), whose
bpcd phenyl groups each contain one ortho hydrogen and deuterium atom. Generation of 1,1-Os<sub>3</sub>(CO)<sub>9</sub>-
(bpcd-<i>d</i><sub>4</sub><i><sub>,ortho</sub></i>) 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 in
the ortho metalation step. Photolysis of 1,1-Os<sub>3</sub>(CO)<sub>10</sub>(bpcd-<i>d</i><sub>4,</sub><i><sub>ortho</sub></i>) at elevated temperature and thermolysis
of the low-temperature photolysis hydride/deuteride mixture afford an equilibrium mixture of hydride
(67%) and deuteride (33%), yielding a <i>K</i><sub>eq</sub> value of 0.49, which in conjunction with the <i>k</i><sub>H</sub>/<i>k</i><sub>D</sub> ratio from
the C−H(D) ortho-metalation step allows us to establish a <i>k</i><sub>H</sub>/<i>k</i><sub>D</sub> value of 0.60 for the reductive coupling
from the participant hydride/deuteride clusters. These data, which represent the first isotope study on ortho
metalation 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 <b>3 </b>→<b> 4</b> provide activation parameters
consistent with the rate-limiting formation of the unsaturated cluster 1,1-Os<sub>3</sub>(CO)<sub>9</sub>(bpcd), preceding the
irreversible P−C cleavage manifold. The ortho metalation of the bpcd ligand in <b>3</b> and formation of the
benzyne moiety <b>4</b> are discussed relative to ligand degradation reactions in this genre of cluster.