Tripod ligands containing a mixed P/N/S donor set: Synthesis and coordination chemistry

Article abstract of DOI:10.1002/cber.19971300917

The preparation of neopentane-based tripod ligands CH₃C(CH₂X)(CH₂Y)(CH₂Z) 3 (X = NR₂, NHR; Y = PR₂; Z = PR₂, SR, S^-) in a convergent manner is described. The procedure is based on the aminolytic cleavage of functionalized oxetanes CH₃C(CH₂OCH₂)CH2R 1 by primary or secondary amines, leading to functionalized amino alcohols CH₃C(CH₂NHR′)(CH₂OH)(CH₂R) or CH₃C(CH₂NR′₂)-(CH₂OH)(CH ₂R) 2. The appropriate activation of the R (e.g. OR) and OH groups present in 2 allows for substitution vs. SR or PR₂ donor functions. Depending on the nature of the groups present in each reaction step, various protection and deprotection steps have to be taken in the course of this type of preparation of the tripod ligands 3. By reaction with (CH₃CN)₃Mo(CO)₃, ligands 3 form Mo(CO)₄ derivatives 4 or Mo(CO)₃ derivatives 5, depending on the reaction condi-tions. In compounds 4, the ligands are coordinated in a bidentate mode with the soft donor atoms (P, S) coordinated and the hard donor function playing the role of the dangling arm. In the trihapto bonding mode present in 5, all three donor functions, two soft (P, S) and one hard (NHR′, NR′2), are coordinated. The two types of coordination compounds may be interconverted: 4e (X = NMe2, Y = PPh2, Z = SiPr) with a non-coordinating CH2NMe2 group is transformed into 5c upon photolytic decarbonylation. Under 1 bar CO at 20°C, 5c reverts to 4e. X-ray structure analysis of a series of compounds of types 4 and 5 reveals characteristics of the relevant conformational patterns. All compounds have been fully characterized by the standard analytical techniques (NMR, MS), as well as elemental analysis. VCH Verlagsgesellschart mbH,.