Ligand based reactions in the chiral tungsten fragment coordination sphere.

摘要

The dramatic effect of an ancillary alkyne ligand on the regioselectivity of nucleophile and electrophile additions to monodentate nitrogen ligands is illustrated by comparison of ligand based reactions in [Tp' (CO)2W]+ and [Tp'(CO)(PhCCMe)W] + coordination spheres. Nitrogen ligands accessible from free nitriles and amines can be interconverted by addition of nucleophiles or electrophiles reveal important pi-bonding interactions for multiply bonded nitrogen ligands are also discussed. Two systems that utilize the [Tp'W(CO)(PhCCMe)] + fragment are the focus of this dissertation, one containing nitrogen donor ligands and the other a methylene carbene moiety.; Starting from free amines, a series of alkyl and aryl amido, imine, azavinylidene, and amine complexes containing the chiral [Tp'W(CO)(PhCCMe)] + fragment have been synthesized. Reaction of Na[HBEt3] with an E/Z mixture of [Tp'W(CO)(PhCCMe)-(NH=CMeEt)] [BAr'4] results in hydride addition at the imine carbon to form the amido complex with high diastereoselectivity reflecting differentiation between methyl and ethyl groups on the substrate imine carbon. A competing reaction forms azavinylidene complex as a minor product via deprotonation of the coordinated imine ligand in the reagent. The ratio of amido to azavinylidene products tracks the E to Z isomer ratio and suggests that different reaction pathways characterize these two isomers. Relative pKa's of the various imine and amine complexes have been measured in THF, and kinetic acidity measurements of related imine complexes have been used to help understand these results.; Cyclic amido and imine complexes based on pyrrolidine have been synthesized and structurally characterized by X-ray crystallography. Addition of Li[DBEt 3] to the cyclic imine complex produces a deuterated amido complex with a diastereomer ratio near one. Addition of alkyl lithium reagents results in formation of an enamido complex by deprotonation of the carbon a to the imine.; The electrophilic reactivity of a methylene carbene complex, [Tp '(CO)(PhCCMe)W=CH2][PF6], was surveyed with both neutral nucleophiles and anionic nucleophiles to give derivatives of the form [Tp'(CO)(PhCCMe)W-CH2-Nu] +,°. The stereochemistry of the single diastereomer of the t-butyl acetoacetate adduct was determined by 2-D NOESY. Cyclohexene sulfide transfers a sulfur atom to the carbene carbon to form a rare pi-bound thioformaldehyde complex.