Metallaheteroborane chemistry. Part 11. Selective syntheses of the palladium heteroborane complexes [2,2-(PR3)2-closo-2,1-PdEB10H10](R3= Ph3, MePh2 or Me2Ph; E = Se or Te) and [2-X-2-(PPh3)-closo-2,1-PdTeB10H9(PPh3)](X = Cl, Br, I, CN, SCN or O2CMe)

Abstract

Reaction of [PdCl₂(PR₃)₂](R₃= Ph₃, MePh₂ or Me₂Ph) with the nido-[7-EB₁₀H₁₁]^– anions (E = Se or Te) in tetrahydrofuran (thf) at ambient temperature affords twelve-vertex [2,2-(PR₃)₂-closo-2,1-PdEB₁₀H₁₀] complexes selectively in yields ranging from 16 (E = Se, R = Ph) to 82%(E = Te, R₃= Me₂Ph). In contrast, the reaction between [PdX₂(PPh₃)₂](X = Cl or I) and [7-TeB₁₀H₁₁]^– in refluxing toluene affords only [2-X-2-(PPh₃)-closo-2,1-PdTeB₁₀H₉(PPh₃)] in 39 and 95% yields respectively. Further reactions of [2-I-2-(PPh₃)-closo-2,1-PdTeB₁₀H₉(PPh₃)] with Hg^II salts in thf produce [2-X-2-(PPh₃)-closo-2,1-PdTeB₁₀H₉(PPh₃)] complexes (X = Cl, Br, CN, SCN or O₂CMe) in yields from 19 (X = O₂CMe) to 96%(X = CN). All complexes were characterised by infrared and NMR spectroscopies. Variable-temperature ¹H-{³¹P} NMR spectroscopy of [2,2-(PMe₂Ph)₂-closo-2,1-PdSeB₁₀H₁₀] shows a metal-to-selenaborane rotational bonding fluxionality with ΔG_‡²⁹³= 44.5 kJ mol^–1. An X-ray diffraction study of [2,2-(PMe₂Ph)₂-closo-2,1-PdTeB₁₀H₁₀]6 reveals the crystals to be monoclinic, space group P2₁/n, with a= 13.110(3), b= 10.498(3), c= 19.561(3)Å, β= 105.44(1)° and Z= 4. A final R factor of 0.023 was calculated for 4579 observed reflections. Principal interatomic distance include Pd–Te 2.6833(2), Pd–B 2.234(3)–2.301(3), Te–B 2.294(4)–2.374(3) and Pd–P 2.3301(7) and 2.3354(8)Å. An X-ray diffraction study of [2-(O₂CMe)-2-(PPh₃)-closo-2,1-PdTeB₁₀H₉(PPh₃)]14 recrystallised from CH₂Cl₂–n-C₇H₁₄ as 14. 0.79CH₂Cl₂ shows the crystals to be triclinic, space group P with a= 10.416(2), b= 12.409(2), c= 18.720(4)Å, α= 75.59(2), β= 84.10(2), γ= 70.98(1)° and Z= 2. The final R factor is 0.035 for 6472 observed reflections. The acetate ligand is monodentate with Pd–O(1) 2.121(3)Å. Other interatomic distances include Pd–Te 2.6903(4), Pd–P(2) 2.355(1), Pd–B(7) 2.201(5), Pd–B(6) 2.268(4) and B(11)–P(1) 1.942(4)Å.