SYNTHESIS AND STRUCTURE OF PHOSPHINOPHOSPHINIDENE-PHOSPHORANES TBU(2)P-P=P(ME)TBU(2)-1, TBU(ME(3)SI)P-P=P(ME)TBU(2)-2, AND TBU(2)P-P=P(BR)TBU(2)-3

A new method for the synthesis of 1 and 2 (Formulae see ''Inhaltsubersicht'') is reported based on the reaction of 5 with substitution reagents (Me(2)SO(4) or CH3CI). The results of the X-ray structure determination of 1 and 2 are given and compared with those of 3. While in 3 one P-P distance corresponds to a double bond and the other P-P distance to a single bond (difference 12.5 pm) the differences of the P-P distances in 1 and 2 are much smaller: 5.28 pm in 1, 4.68 pm in 2. Both 1 and 2 crystallize monoclinic in the space group P2(1)/n (Z = 4). 2 additionally contains two disordered molecules of the solvent pentane in the unit cell. Parameters of 1: a = 884.32(8) pm, b = 1924.67(25) pm, c = 1277.07(13)pm, beta = 100.816(8)3 and of 2: a = 1101.93(12) pm, b = 1712.46(18) pm, c = 1395.81(12)pm, beta = 111.159(7)degrees, all data collected at 143 K. The skeleton of the three P atoms is bent (PPP angle 100.95 degrees for 1, 100.29 degrees for 2 and 105.77 degrees for 3). Ab initio SCF calculations are used to discuss the bonding situation in the molecular skeleton of the three P atoms of 1 and 3. The results show a significant contribution of the ionic structure R(2)P-P((-))-P((+))(X)R(2). The structure with (partially) charged P atoms is stabilized by bulky polarizable groups R (as tBu) as compared to the fully covalent structure R(2)P-P(X)-PR(2).