Ammoniacal Synthesis of Lanthanum Aryloxide Complexes and Observation of a Unique Interconversion between Oxygen- and .eta.-Arene-Bridged Dimeric Species. X-ray Crystal Structures of La2(OAr)6(NH3)n (n = 0, 2), La(OAr)3(NH3)4, and La(OAr)3(THF)2 (Ar = 2,6-i-Pr2C6H3)

Abstract

Reaction of LaCl{sub 3} with 3 equiv of sodium metal in liquid ammonia at -78 {degrees}C, followed by addition of 3 equiv of HOAr (Ar = 2,6-i-Pr{sub 2}C{sub 6}H{sub 3}) in toluene produces La(OAr){sub 3}(NH{sub 3}){sub x} (1) after warming to room temperature. Dissolution of 1 in toluene followed by 6 h reflux provides La{sub 2}(OAr){sub 6} (2) in good yield. An X-ray crystallographic study revealed that 2 contains a dimeric unit held together with two {eta}{sup 6}-arene bridges formed from aryloxide ligands with La-C(av) = 3.062(10) {Angstrom}. The La-O distances average 2.193(5) and 2.273(5) {Angstrom} for terminal and bridging aryloxide ligands, respectively. Dissolution of 1 in toluene followed by vacuum filtration and crystallization from toluene without reflux yields La{sub 2}(OAr){sub 6}(NH{sub 3}){sub 2}(3) in high yield. The X-ray crystal structure of 3 reveals an alternate dimeric structure bridged by oxygen atoms of the aryloxide ligands. X-ray crystallography has shown that a third compound may be isolated by gravity filtration and crystallization of 1 to produce La(OAr){sub 3}(NH{sub 3}){sub 4} (4). 4 displays a capped pseudo-octahedral geometry around the metal center with facial aryloxide ligands average 2.252(6) {Angstrom}. The La-N distances for the NH{sub 3} ligands average 2.750(9) {Angstrom} withmore » no significant lengthening of the capped La-N bond.« less