Coordination and Dehydrogenation of Diphosphine-Borane Ph2PCH2PPh2·BH3 at a Heterometallic MoRe Center to Give an Agostic Boryl-Bridged Derivative

The coordination chemistry of the title diphosphine-borane adduct at heterometallic MoRe centers was examined through its reactions with the hydride complex [MoReCp(μ-H)(μ-PCy₂)(CO)₅(NCMe)] (Cp = η⁵-C₅H₅). The latter reacted rapidly with stoichiometric amounts of dppm·BH₃ (dppm = Ph₂PCH₂PPh₂) in refluxing toluene solution, with displacement of the nitrile ligand, to give [MoReCp(μ-H)(μ-PCy₂)(CO)₅(κ¹_P-dppm·BH₃)], with a P-bound diphosphine-borane ligand arranged trans to the PCy₂ group. Decarbonylation of the latter complex was accomplished rapidly upon irradiation with visible-UV light in toluene solution at 263 K, to give the agostic derivative [MoReCp(μ-H)(μ-PCy₂)(CO)₄(κ¹_P,η²-dppm·BH₃)] as major product (Mo-Re = 3.2075(5) Å), along with small amounts of the diphosphine-bridged complex [MoReCp(μ-H)(μ-PCy₂)(CO)₄(μ-dppm)]. Extended photolysis of the agostic complex at 288 K promoted an unprecedented dehydrogenation process involving the borane group and the hydride ligand, to give the diphosphine-boryl complex [MoReCp(μ-η²:κ²_P,B-H₂B·dppm)(μ-PCy₂)(CO)₄] (Mo-Re = 3.075(1) Å). The latter displayed a boryl ligand in a novel bridging coordination mode, it being σ-bound to one of the metal atoms (B-Re = 2.38(2) Å) while interacting with the second metal atom via a strong side-on tricentric B-H-M interaction (B-Mo = 2.31(1); H-Mo = 1.9(1) Å). The overall dehydrogenation process was endergonic by 43 kJ/mol, according to density functional theory calculations.

Chiral alkaline earth metal complexes with M–Se direct bond (M = Mg, Ca, Sr, Ba): syntheses, structures and ε-caprolactone polymerisation

Synthesis and structural details of enantiomerically pure alkaline earth metal complexes (Mg, Ca, Sr, Ba) supported by chiral phosphinoselenoic amides are reported.

Synthesis, characterization and reactivity of potassium and barium complexes containing phosphane-borane stabilized methanides

The polymeric potassium complex [K{CH(PPh2BH3)2}]∞ (1) was prepared and used as a starting material for the syntheses of related N,N,N',N'-tetramethylethylenediamine (tmeda) and N,N,N',N',N''-pentamethyldiethylenetriamine (pmdta) ligated potassium derivatives [K{CH(PPh2BH3)2}(tmeda)2]∞ (2) and [K{CH(PPh2BH3)2}(pmdta)]2 (3). Salt metathesis reactions with [BaI2(thf)5] allowed the synthesis of the barium derivatives [BaI{CH(PPh2BH3)2}(thf)5] (5) and [Ba{CH(PPh2BH3)2}2(solv)2}] (solv = Et2O, thf) (6), which are more prone to subsequent reactions than the potassium derivatives. One of the resulting products, [Ba4O{CH(PPh2BH3)2}3{Ph2PCH(BH3)PPh2BH3}3] (7), which contains two different isomeric forms of the bis(borane) adduct of Ph2PCHPPh2, was isolated. The complexes were characterized by NMR techniques and single crystal X-ray diffraction measurements.

Formation of a Ph2PCH(BH3)P(BH3)Ph2 ligand via formal 1,2-borane migration

The transfer of the anionic Ph(2)P(BH(3))-CH-P(BH(3))Ph(2) ligand from potassium to barium results in the subsequent formation of a tetranuclear barium cluster which contains the hitherto unknown isomeric form Ph(2)P-CH(BH(3))-P(BH(3))Ph(2) of the ligand.