Using 13 C, 1 H and 19 F NMR spectroscopy, formation of cationic species was studied in ternary systems (SBI)ZrX 2 /AlBu i 3 / [CPh 3 ][B(C 6 F 5 ) 4 ], where X = Cl, Me [(SBI) = rac-Me 2 Si(Ind) 2 ]. In the first system (X = Cl), the ion pair [(SBI)Zr(l-Cl) 2 Zr(SBI)]-[B(C 6 F 5 ) 4 ] 2 (IV) predominates at low Al/Zr ratios (Al/Zr < 10), whereas at higher Al/Zr ratios (P20) in the absence of monomer mainly [(SBI)Zr(l-H)(l-C 4 H 7 )AlBu i 2 ] [B(C 6 F 5 ) 4 ] (V) is formed. The binuclear complex [(SBI)Zr(l-Cl) 2 Zr(SBI)][B(C 6 F 5 ) 4 ] 2 has been characterized crystallographically. Species V is also formed in the system X = Me at high Al/Zr ratios. In the presence of AlBu i 3 , IV displays activity in propylene polymerization and is the most likely precursor of the polymerizing species. Consistent mechanisms have been proposed for the reactions in these catalytic systems.

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Hypervalence, Phosphines, Lewis Acid-Base AdductsLewis acid-base adducts between NMe3, tmeda (A^A^Af'-tetramethylethylenediamine), and 1.4-dimethylpiperazine as donors and PBr3 as acceptor have been prepared and structurally characterized. NMe3 and tmeda form 1:1 adducts (Me3 N)PBr3 (1) and (tmeda)PBr3 (2), re spectively, while 1,4-dimethylpiperazine adds 2 molecules of PBr3 leading to [(1,4-dimethylpiperazine)(PBr3):] (3). Adduct 2 is found in two modifications 2a and 2b with different crystal and molecular structures. (Crystal data of 1: monoclinic P2\/n, a = 5.983(3), b = 10.821(2), c = 13.877(5) Ä, ß = 99.70(2)°, Z = 4. 2a: monoclinic P2i/c, a = 7.891(1), b = 12.826(1), c = 12.218(2) A ,ß = 102.162(6)°, Z = 4. 2b: monoclinic P2]/n, a = 11.687(2), b = 8.375(1), c = 12.668(1) A, ß = 102.74(1)°, Z = 4. 3: monoclinic P2Jc, a = 6.383(3), b = 16.36(3), c = 8.407(3) A,ß= 101.49(2)°, Z= 2). The molecular structures of 1 and 2 indicate a partially ionic character with a strongly bonded amine and one (1 ) or two (2 ) weakly bonded bromine atoms. In 2 the donor tmeda is bonded through both nitrogen atoms to one phosphorus atom. In 3 the 1.4-dimethylpiperazine ring is in chair conformation, the methyl and PBr3 substituents being in equatorial and axial positions, respectively. Due to axial-axial repulsion the N-P donor-acceptor bonds are long while the P-Br bonds are rather uniform in length.

The complexation potential of mono(borane)diorganophosphides toward lithium and aluminum has been explored in the complexes [{(tmeda)Li}{P(BH3)Me2}] (1), [{((−)-sparteine)Li}{P*(BH3)(Ph)tBu}] (2), [(tmeda)2Li]+[Al{P(BH3)Me2}4]- (3), and [(mtbe)Li]+[Al{P(BH3)Me2}4]- (4) (tmeda = N,N,N ‘,N ‘-tetramethylethylenediamine; mtbe = methyl-tert-butyl ether). In 1 there is competing Li−P and Li−H−B bonding, while in 2 Li−P coordination is absent due to steric hindrance. Compound 2 contains the enantiomerically pure P-chiral anion [P*(BH3)(Ph)tBu]-, which is a valuable building block for the synthesis of P-chirogenic phosphines. The complexes 3 and 4 are the first homoleptic tetraphosphorus aluminates to be structurally characterized.

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