DEMETALATION OF A DIMOLYBDENUM CYCLOTETRAPHOSPHOXANE CAGE COMPLEX AND SYNTHESES OF HETEROBIMETALLIC CAGES

Selective excision of the Mo-II vertex in the mixed-valent, adamantanoid cage complex Mo(CO)(4)[(Pr2NPO)-Pr-i]Mo-4(CO)(2)I-2 with sodium dithiocarbamate yielded the metalla ligand Mo(CO)(4)[(Pr2NPO)-Pr-i](4) (1). Complex 1 has been characterized by spectroscopy and by X-ray crystallography. Its structure retains the parent adamantane framework except for the vacant metal vertex. Significant distortions of the P4O4 core are noted with [Mo]-P-O bonds (1.623 (4) Angstrom) shortened at the expense of the uncoordinated P-O bonds (1.671 (4) Angstrom). Nucleophilic attack by primary alcohols (ROH) on 1 led to cleavage of a single P-O-P bond to give Mo(CO)(4)[((i)Pr(2)MPO)(2)((i)Pr(2)NPOR)((Pr2NP)-Pr-i(O)H)] (R = Me, 3a; R = Et, 3b); the postulated monocyclic structure of 3a has been confirmed by X-ray crystallography. Synthetically the covergent lone pairs in 1 enabled formation of new heterobimetallic cage complexes of the type Mo(CO)(4)[(Pr2NPO)-Pr-i](4)M (4a-g; M = Cr(CO)(4), Fe(CO)(3), NiBr2, PtCl2, Cu(MeCN)(2)BF4, AgNO3, PdBr2). The molecular structure of Mo(CO)(4)[(Pr2NPO)-Pr-i]4NiBr2 (4c) has been determined. A pseudotetrahedral coordination geometry was observed at the paramagnetic Ni-II center, and the P4O4 core was found to have readjusted to its electronic demands. Comparison of the spectral properties of the conserved Mo(CO)(4) moiety in these products suggests a small but observable transmission of intracage influence from the heterometal. Treatment of 4c with iron pentacarbonyl led to reduction of the nickel vertex and formation of the diamagnetic complex Mo(CO)(4)[(Pr2NPO)-Pr-i]Ni-4(CO)(2) (6). Competitive chlorination and iodination of 6 revealed preferential halogenation at the nickel site.