Synthesis and Spectroscopic and X-ray Structural Characterization of Compounds Involving Boron-Phosphorus Multiple Bonds: Lithium Salts of Boryl Phosphides and Their Precursors

Article abstract of DOI:10.1021/ja00186a023

The synthesis and spectroscopic and structural characterization of several lithium salts of boryl phosphides and their precursors are described.Treatment of the lithium salt of a primary phosphane H2PR' with R2BX (X = F, Cl) affords the phosphinoboranes (borylphosphanes) R2BPHR' (R/R' =Ph/t-Bu (1), Mes/t-Bu (2), Trip/t-Bu (3), Mes/Ph (4), Mes/Cy (5), Mes/Mes (6) (Mes = 2,4,6-Me3C6H2, Trip = 2,4,6-i-Pr3C6H2, Cy = cyclohexyl) in good yield.The reaction of compounds 1-6 with 1 equiv of n-BuLi or t-BuLi affords their corresponding lithium salts (7-12).The addition of 2 equiv of 12-crown-4 to Li(Et2O)2PR'BMes2 (R' = Ph (10), Cy (11), Mes (12)) gives the solvent-separated salts *THF (R' = Ph (13), Cy (14), Mes (15)).Also, the reaction of Mes2BF with 2 gives (16) with elimination of Me3SiF rather than LiF.In addition, the reaction between TripBBr2 and 2 equiv of LiPHMes gave the lithium salt (17), involving boron bound to two phosphorus centers throuhg a single and a multiple bond.Apart from (11)B and (31)P NMR spectroscopic characterization, the X-ray structures of the dimeric compound 1, the lithium salts (9), (16), and (17) are described.Compounds 10-12 and 13-15, including the structures of 11, 12, and 15, have been described in a preliminary communication.The lithium compounds 7-17 are of particular interest because they are the only structurally characterized compounds known to involve a high degree of multiple bonding between boron and phosphorus.Thus, compound 17 is also notable since it has theshortest B-P bond length, 1.810(3) Angstroem, reported to date.Crystal data with Mo Kα radiation (λ=0.71069 Angstroem) at 130 K: 1, a=10.291(4) Angstroem, b=10.468(3) Angstroem, c=14.767(2) Angstroem, α=71.05(2) deg, β=75.63(2) deg, γ=82.49(3) deg, triclinic, space group P<*>, Z=2, R=0.049; 9, a=10.378(4) Angstroem, b=19.094(6) Angstroem, c=21.995(7) Angstroem, orthorhombic Pc2₁n, Z=4, R=0.036; 16, a=10.331(6) Angstroem, b=16.133(5) Angstroem, c=10.647(5) Angstroem, β=95.13(4) deg, monoclinic, space group P2₁, Z=2, R=0.049; 17, a=13.543(2) Angstroem, b=17.812(3) Angstroem, c=17.475(3) Angstroem, β=93.72(1) deg, monoclinic, space group P2₁/n, Z=4, R=0.063.