Barium complexes with crown-ether-functionalised amidinate and iminoanilide ligands for the hydrophosphination of vinylarenes.

The detailed multistep syntheses of two nitrogen-based sterically congested iminoanilidine and amidine proligands bearing a tethered 15-member aza-ether-crown macrocycle, namely {I^Acrown}H and {Amcrown}H, are reported. These proligands react with [Ba{N(SiMe2H)2}2·(thf)n] to generate the heteroleptic barium complexes [{I^Acrown}BaN(SiMe2H)2] (5) and [{Amcrown}BaN(SiMe2H)2] (6) in high yields. These complexes exhibit high coordination numbers (resp. eight and seven) and are in addition stabilised by mild BaH-Si interactions. Unusually for oxophilic elements such as barium, the amidinate ligand in 6 is only η1-coordinated. Complexes 5 and 6 mediate the intermolecular hydrophosphination of styrene with primary (PhPH2) and secondary (HPPh2) phosphines. Their catalytic performance compares favourably with those of other barium precatalysts for these reactions. During the course of the hydrophosphination of styrene with HPPh2 catalysed by 5, the phosphide complex [{I^Acrown}BaPPh2] (7) could be intercepted and crystallographically characterised.

Metal⋠⋠⋠F-C Bonding in Low-Coordinate Alkaline Earth Fluoroarylamides.

A set of calcium and barium complexes containing the fluoroarylamide N(C6 F5 )2 - is presented. These compounds illustrate the key role of stabilising M⋅⋅⋅F-C secondary interactions in the construction of low-coordinate alkaline earth complexes. The nature of Ca⋅⋅⋅F-C bonding in calcium complexes is examined in the light of structural data, bond valence sum (BVS) analysis and DFT computations. The molecular structures of [Ca{N(C6 F5 )2 }2 (Et2 O)2 ] (4'), [Ca{µ-N(SiMe3 )2 }{N(C6 F5 )2 }]2 (52 ), [Ba{µ-N(C6 F5 )2 }{N(C6 F5 )2 }⋅toluene]2 (62 ), [{BDIDiPP }CaN(C6 F5 )2 ]2 (72 ), [{N^NDiPP }CaN(C6 F5 )2 ]2 (82 ), and [Ca{µ-OB(CH(SiMe3 )2 )2 }{N(C6 F5 )2 }]2 (92 ), where {BDIDiPP }- and {N^NDiPP }- are the bidentate ligands CH[C(CH3 )NDipp]2 - and DippNC6 H4 CNDipp- (Dipp=2,6-iPr2 -C6 H3 ), are detailed. Complex 62 displays strong Ba⋅⋅⋅F-C contacts at around 2.85 Å. The calcium complexes feature also very short intramolecular Ca-F interatomic distances at around 2.50 Å. In addition, the three-coordinate complexes 72 and 82 form dinuclear structures due to intermolecular Ca⋅⋅⋅F-C contacts. BVS analysis shows that Ca⋅⋅⋅F-C interactions contribute to 15-20 % of the bonding pattern around calcium. Computations demonstrate that Ca⋅⋅⋅F-C bonding is mostly electrostatic, but also contains a non-negligible covalent contribution. They also suggest that Ca⋅⋅⋅F-C are the strongest amongst the range of weak Ca⋅⋅⋅X (X=F, H, Cπ ) secondary interactions, due to the high positive charge of Ca2+ which favours electrostatic interactions.

Heterobimetallic Ba/Li and Ca/Li amides and diphenylmethanide.

The structures of the heterobimetallic Ca/Li and Ba/Li amides [CaLi2{µ2-N(SiMe2H)2}4]∞ and [Ba2Li2{µ2-N(SiMe2H)2}6]∞, stabilised by metalH-Si interactions, and that of a diphenylmethanide calcium salt, [Li(tmeda)2+·Ca(CHPh2)3(thf)-], are presented. These well-defined, storable compounds are inert towards Et2O and thf.