209907-37-9Relevant academic research and scientific papers
Complex kinetics of simple substitution reactions of Os3(CO)9(μ-C4Ph4) with smaller P-donor nucleophiles
Po?, Anthony J.,Moreno, Consuelo
, p. 5518 - 5530 (1999)
The osmacyclopentadiene ring in the triangular Os3 cluster Os3(CO)9-(μ-C4Ph4) bridges two of the Os atoms and is found to activate associative attack at the third Os atom (which is in an Os(CO)4 moiety) by a factor of ～109 compared with reactions of the parent cluster Os3-(CO)12. The overall reactions in heptane of 17 P-donor nucleophiles with Tolman cone angles θ ≤ 143° lead to substitution at the Os(CO)4 center in three rapid but kinetically observable stages: (i) reversible attack by a nucleophile to form an adduct in which an Os-Os bond in the cluster has been broken, (ii) loss of CO and formation of a new closed Os3 cluster, and, usually, (iii) isomerization of the initially formed cluster to form the final substituted product. The dependence of the rates on the σ-basicity and size of the nucleophiles shows that the standard reactivity toward adduct formation is very high, only high nuclearity clusters that contain encapsulated C atoms being known to react faster. Nucleophiles with θ ≤ 120 ± 4° react at rates that are independent of their size and that increase substantially with their σ-basicity. When the cone angles are larger, steric retardation is observed. Equilibrium constants for adduct formation by 14 of the nucleophiles were obtained from the rates of adduct formation and loss of L from the Os3(CO)9L(μ-C4Ph4) adducts and by two other methods. Loss of CO or L from the adducts becomes slower the greater the net donicity of the ligands but is essentially independent of ligand size. Rates of isomerization of the initial product are not very precise and are not appreciably sensitive to the nature of the ligands. Activation parameters were obtained for reactions involving five of the nucleophiles, and these, together with the magnitudes of the electronic and steric effects, can lead to estimates of the contributions of bond making and bond breaking in the transition states.
Steric limitations in associative substitution reactions of Os3(CO)9(μ-C4Ph4)
Poe, Anthony J.,Farrar, David H.,Ramachandran, Ravindranath,Moreno, Consuelo
, p. 82 - 89 (2008/10/08)
Reactions of the cluster Os3(CO)9(μ-C4Ph4) (1) with a large number of smaller P-donor nucleophiles (Tolman cone angle θ ≤ 143°) proceed rapidly in heptane at room temperature via associative adduct formation to form the monosubstituted products. However, reactions with several larger P-donor nucleophiles (θ ≤ 145°) in heptane at room temperature yield, in a single observable bimolecular step, a mixture of mononuclear and dinuclear products and it is therefore not possible to synthesize the monosubstituted clusters directly with these larger ligands. Crystallographic structures of Os3(CO)8(etpb)(μ-C4Ph 4)·(CH3OH) (2etpb) (etpb = P(OCH2)3CEt) and Os3(CO)8-(P(OPh)3)(μ-C4Ph 4)·(C6H14) (2P(OPh)3) have been determined and show that the substituent has displaced a CO ligand from the Os(CO)4 moiety in 1.
