COMPLEXATION OF BIS(P-TERT-BUTYLPHENYL)MAGNESIUM WITH 1,3-XYLYLENE CROWN-ETHERS AND GLYMES

The complexation of bis(p-tert-butylphenyl)magnesium (9) with a series of polyether ligands was studied. Crystal structures of 9.[1,3-xylyle ne-18-crown-5] (8), 2 9.[1,3,16,18-dixylylene-30-crown-8] (11), 9.[dig lymel (12), and 9.[tetraglymel (13) were determined. Complex 8 has a ' 'rotaxane'' structure (8a) with hexacoordinated magnesium, analogous t o that found previously for Ph2Mg.[1,3-xylylene-18-crown-5] (1a); this provides additional evidence for the dissociative mechanism proposed earlier for rotaxane formation, as does an NMR investigation of 1 and 8 in solution. The thermodynamic parameters for the equilibrium 8b rev ersible 8a were determined by temperature dependent H-1 NMR spectrosco py as DELTAH(eq) = -5 kJ mol-1 and DELTAS(eq) = -17 mol-1 K-1. It was anticipated that in 11, two diarylmagnesium moieties could be accommod ated within the large crown ether. However, in the 2:1 complex, the tw o magnesiums are not located inside the crown ether cavity, but each i nteracts at the outside of the crown ether with three adjacent oxygen atoms of a polyether chain and becomes pentacoordinated; the large cro wn ether ring is folded ''inside out'', thus facilitating this ''side- on'' bonding of the two Ar2Mg units. In 12, magnesium is also pentacoo rdinated, while in 13, the magnesium is pentacoordinated to three adja cent oxygens of the five available, including the one of the methoxy g roup; apparently, in both 12 and 13 coordinative saturation has been r eached within the limits of steric restraints. Complex 8: space group P1BAR, a = 11.1949(1) angstrom, b = 11.999(1) angstrom, c = 15.302(1) angstrom, alpha = 73.20(1)degrees, beta = 88.00(2)degrees, gamma = 77. 57(1)degrees, R = 0.066. Complex 11: space group P1BAR, a = 11.453(1) angstrom, b = 13.696(1) angstrom, c = 14.217(1) angstrom, alpha = 111. 40(1)degrees, beta = 102.97(1)degrees, gamma = 101.77(1)degrees, R = 0 .067. Complex 12: space group C2/c, a = 23.530(3) angstrom, b = 8.821( 1) angstrom, c = 12.731(2) angstrom, beta = 97.26(1)degrees, R = 0.062 . Complex 13: space group P1BAR, a = 12.727(1) angstrom, b = 15.268(1) angstrom, c = 24.194(2) angstrom, alpha = 98.52(1)degrees, beta = 93. 49(1)degrees, gamma = 99.75(1)degrees, R = 0.057.