Charles B. Dobson

Solid state structure and reactivity in solution. 8. Implications of the structure of [1,2-bis(diphenylphosphino)ethane] tetra-carbonylmolybdenum(0) to the chelate effect

Abstract The structure of (diphos)Mo(CO)4 (diphos=1,2- bis(diphenylphosphino)ethane) has been determined by single crystal X-ray crystallography. The crystals are orthorhombic with a=22.600(8), b=16.799(4) and c=14.587(4) A, space group Pbca, Dcalc.=1.45 g cm−3 and Z=8. The structure was solved by the Patterson technique and refined by full-matrix least- squares methods to R=0.044 using 2206 reflections measured on a four-circle diffractometer. The coordination about the central molybdenum atom is a distorted octahedron, the greatest deviation from ideal geometry being the P1-Mo-P2 angle (80.2(1)°). Other distortions are induced through steric interaction between the phenyl and the carbonyl groups. The structure of (diphos)Mo(CO)4 is compared to that previously reported for cis- (MePh2P)2Mo(CO)4; the two molecules differ only that two methyl groups of the latter complex are replaced by the CH2CH2 backbone in the former. The influence of this difference is discussed both in terms of molecular distortions induced by the presence of the chelate ring and their influence on reactivity via chelate ring-opening and -closure.

Silicon diffusion characteristics of different surface imaging resists

This paper describes a study of the silylation characteristics of different resists that are suitable for single-layer, surface-imaging patterning applications. In particular, the effect of different process parameters on the silicon diffusion in UCBs Plasmask®resist is discussed. The diffusion profile of silicon in the resist is decorated by a staining technique followed by SEM analysis. This allows for two-dimensional resolution of the diffusion profiles and the observation of other process attributes. Links are established among exposure, silylation and etch by observing silylated profiles. It is shown that the silylation profile characteristics are dominated by the resist image created during exposure. Also, the effects of post-exposure bake and silylating agent temperature are presented. Diffusion profiles for MacDermids PR1024 are also shown.

Octahedral metal carbonyls: XL. Rates of olefin coordination via chelate ring-closure in cis-[(η1-4-pentenyldiphenylphosphine)tetracarbonyltungsten(0)] created through flash photolysis☆

Abstract Ring-closure via olefin coordination in coordinatively-unsaturated cis -[(η 1 -pdpp)W(CO) 4 ], (pdpp = CH 2 CH(CH 2 ) 3 P(C 6 H 5 ) 2 , 4-pentenyldiphenylphosphine) produced via pulsed laser flash photolysis of cis -(pip)(η 1 -pdpp)W(CO) 4 (pip = piperidine) in chlorobenzene has been identified unequivocally. Rates and activation parameters for this pathway and for competitive bimolecular interaction of pip at the solvated coordination site have been measured.

Octahedral metal carbonyls 75. ‘Directed’ synthesis of tungsten carbonyl complexes of alkenyldiphenylphosphines

Abstract Alkenyldiphenylphosphines, CH 2 CH(CH 2 ) n PPh 2 (alkP; n =1-4), react with c is-(pip) 2 W(CO) 4 (pip=piperidine) to afford cis -(pip)(alkP)W(CO) 4 complexes in which alkP is coordinated through P. Two of these complexes ( n =2, 3) react via chelate ring closure either photochemically or thermally to afford, in high yield, (ηn 3 -alkP)W(CO) 4 products in which alkP functions as a chelating ligand; for the other two ( n =1, 4), such products were observed in solution but could not be isolated. In contrast to observations for other complexes containing both phosphine and olefin functionalities, olefin bond migration was not observed to take place. This observation is attributed the ‘direction’ of the syntheses, which, for olefin bond migration to take place requires initial coordination of the alkP ligands through CC rather than through P. The influence of the nature of the chelate ring backbone on the outcome of such reactions is also discussed.

Octahedral metal carbonyls. 58. Rate constants for ring-displacement in metal carbonyl complexes containing 5- and 6-membered chelate rings coordinating through sulfur

Mecanisme de la reaction de (DTN)W(CO) 4 avec le triisopropylphosphite dans le chlorobenzene (DTN=tetramethyl-2,2,8,8 dithianonane)

A kinetics method for the identification of coordinatively-unsaturated substituted metal carbonyl transients: cis-[(triphenylphosphine)tetracarbonyltungsten(O)]☆

The specifically solvated five-coordinate intermediate [(triphenylphosphine)-tetracarbonyltungsten(O)] was produced via pulsed laser flash photolysis from cis-(piperi-dine)(triphenylphosphine)tetracarbonyltungsten(O) in chlorobenzene. This five-coordinate species was identified through comparison of the “competition ratio” k2/k−1, for its interaction with piperidine (governed by k−1) and tri(isopropyl) phosphite (governed by k2) as determined through parallel flash photometric and thermal studies. This method offers a broadly applicable means of identification of transients generated upon flash photolysis and of obtaining values of all rate constants for ligand-displacement reactions of substituted octahedral metal carbonyls by Lewis bases.

Solid-state structure and reactivity in solution. V: Ring-closure in the (η1-2,2,8,8-tetramethyl-3,7-dithianonane) tetracarbonyltungsten(0) intermediate

Abstract Pulsed laser flash photolysis of (η2-DTN)W(CO)4 (I, DTN = 2,2,8,8-tetramethyl-3,7-dithianonane) in 1,2-dichloroethane induces ring-opening to afford the solvated [(η1-DTN)W(CO)4] intermediate II. Rates of unimolecular ring-closure for this intermediate to afford I and of bimolecular combination of I with triisopropyl phosphite (L) have been determined, as have activation parameters for the ring-closure pathway. The relatively high enthalpy of activation (12.0(6) kcal/mol) suggests distortion in I induced upon chelate ring-closure. Rates of interaction of L at an “open” coordination site (one produced via CO loss from an octahedral (chelate)M(CO)4 complex) are some two orders of magnitude faster than are those for a “shielded” site produced through ring-opening, suggestive of extensive steric interaction between the bidentate ligand and L for the combination process in the latter.

Preliminary communicationSolid-state structure and reactivity in solution: V. Ring-closure in the (η1-2,2,8,8-tetramethyl-3,7-dithianonane)tetracarbonyltungsten(0) intermediate☆

Abstract Pulsed laser flash photolysis of (η2-DTN)W(CO)4 (I, DTN = 2,2,8,8-tetramethyl-3,7-dithianonane) in 1,2-dichloroethane induces ring-opening to afford the solvated [(η1-DTN)W(CO)4] intermediate II. Rates of unimolecular ring-closure for this intermediate to afford I and of bimolecular combination of I with triisopropyl phosphite (L) have been determined, as have activation parameters for the ring-closure pathway. The relatively high enthalpy of activation (12.0(6) kcal/mol) suggests distortion in I induced upon chelate ring-closure. Rates of interaction of L at an “open” coordination site (one produced via CO loss from an octahedral (chelate)M(CO)4 complex) are some two orders of magnitude faster than are those for a “shielded” site produced through ring-opening, suggestive of extensive steric interaction between the bidentate ligand and L for the combination process in the latter.

Solid-state structure and reactivity in solution

Abstract Pulsed laser flash photolysis of (η2-DTN)W(CO)4 (I, DTN = 2,2,8,8-tetramethyl-3,7-dithianonane) in 1,2-dichloroethane induces ring-opening to afford the solvated [(η1-DTN)W(CO)4] intermediate II. Rates of unimolecular ring-closure for this intermediate to afford I and of bimolecular combination of I with triisopropyl phosphite (L) have been determined, as have activation parameters for the ring-closure pathway. The relatively high enthalpy of activation (12.0(6) kcal/mol) suggests distortion in I induced upon chelate ring-closure. Rates of interaction of L at an “open” coordination site (one produced via CO loss from an octahedral (chelate)M(CO)4 complex) are some two orders of magnitude faster than are those for a “shielded” site produced through ring-opening, suggestive of extensive steric interaction between the bidentate ligand and L for the combination process in the latter.