PYRAZOLE AS A DONOR FUNCTION IN NEOPENTANE-BASED TRIPOD LIGANDS RCH2C(CH(2)PYRAZOL-1-YL)(3-N)(CH2PR2)(N) - SYNTHESIS AND COORDINATION CHEMISTRY

The chlorine functions of CH3C(CH2Cl)(3), 1, may be replaced by pyrazo lyl (pz) as well as imidazolyl (im) residues under the conditions of n ucleophilic substitution leading to tripodal ligands CH3C(CH2X)(3), X = pz, 2; X = im, 3. As a means of introducing two nitrogen donors and one phosphorus donor into a tripod ligand, substitution of the Br and OMs functions in O(CH2)(2)C(CH2Br) (CH2OMs), 8, by nitrogen nucleophil es and subsequent cleavage of the oxetane ring by a phosphide nucleoph ile to give HOCH2C(CH2PPh2) (CH2X)(2) has been developed, furnishing 1 0a (X=pz) and 10d (X=NEt2), respectively. For the synthesis of 10a, K- pz was used as the nucleophile, while 10d was prepared using azide in the initial step, which then had to be transformed into NEt2 in two su bsequent steps. The nucleophugic functions of the oxetane 8 undergo se lective substitution by K-pz and KPPh2 in THF to produce O(CH2)(2)C(CH 2PPh2)(CH(2)pz), 9b. Phosphide cleavage of the oxetane function leads to HOCH2C(CH2PPh2)(CH2PR2)(CH(2)pz), R = Ph, 10b; R = 3,5-Me-2(C6H3), 10c. - The tris(pyrazolyl) tripod ligand 2 reacts with (MeCN)(3)Mo(CO) (3) to give 2 Mo(CO)(3)(MeCN), 12a, in which only two of the three don or functions are coordinated. Upon reaction with 10a, the same reagent gives 10a Mo(CO)(4), 12b, with one pyrazolyl coordinated and the othe r involved in intramolecular hydrogen bonding to the CH,OH function (N ...H-O distance 280 pm). Blocking of the OH function of 10a by etherif ication, i.e. to form EtOCH2C(CH2PPh2)(CH(2)pz)(2), 11, does not drama tically affect the coordination capabilities with 11 Mo(CO)(3)(MeCN), 12d, being formed upon treatment with (MeCN3)(3)Mo(CO)(3). Again only one pz function is coordinated to the metal. Bidentate coordination by two phosphorus donors of 10c is observed in 10c Mo(CO)(3)(MeCN), 12d, The dangling arm pz donor function and the CH2OH group are intermolec ularly hydrogen-bonded in this case. When the bulky P[3,5-Me-2(C6H3)]( 2) substituent of 10c is replaced by the less sterically demanding PPh , donor in 10b, eta(3)-coordination is finally observed with the forma tion of 10b Mo(CO)(3), 13. The coordination capabilities of the new Li gands are rationalized in terms of the size (six-, seven-, and eight m embered rings) and interference of the chelate cycles. All compounds h ave been characterized by the usual analytical and spectroscopic metho ds, with a complete assignment of the NMR data achieved by a combinati on of 2D-NMR techniques in some cases. The structures of the coordinat ion compounds have additionally been deduced by X-ray methods.