Anatomy of Phobanes. Diastereoselective Synthesis of the Three Isomers ofn-Butylphobane and a Comparison of their Donor Properties

Abstract

Three methods for the large scale (50-100 g) separation of the secondary phobanes 9-phosphabicyclo[3.3.1]nonane (s-PhobPH) and 9-phosphabicyclo[4.2.1]nonane (a-PhobPH) are described in detail. Selective protonation of s-PhobPH with aqueous HCl in the presence of a-PhobPH is an efficient way to obtain large quantities of a-PhobPH. Selective oxidation of a-PhobPH in an acidified mixture of a-PhobPH and s-PhobPH is an efficient way to obtain large quantities of s-PhobPH. The crystalline, air-stable phosphonium salts [s-PhobP(CH(2)OH)(2)]Cl and [a-PhobP(CH(2)OH)(2)]Cl can be separated by a selective deformylation with aqueous NaOH. a-PhobPH is shown to be a(5)-PhobPH in which the H lies over the five-membered ring. The isomeric a(7)-PhobPH has been detected but isomerizes to a(5)-PhobPH rapidly in the presence of water. s-PhobPH is more basic than a-PhobPH by about 2 pK(a) units in MeOH. Treatment of s-PhobPH with BH(3).THF gives s-PhobPH(BH(3)) and similarly a-PhobPH gives a(5)-PhobPH(BH(3)). Isomerically pure s-PhobPCl and a(5)-PhobPCl are prepared by reaction of the corresponding PhobPH with C(2)Cl(6). The n-butyl phobane s-PhobPBu is prepared by nucleophilic (using s-PhobPH or s-PhobPLi) and electrophilic (using s-PhobPCl) routes. Isomerically pure a(5)-PhobPBu is prepared by treatment of a-PhobPLi with (n)BuBr and a(7)-PhobPBu is prepared by quaternization of a-PhobPH with (n)BuBr followed by deprotonation. From the rates of conversion of a(7)-PhobPBu to a(5)-PhobPBu, the DeltaG(double dagger) (403 K) for P-inversion is calculated to be 38.1 kcal mol(-1) (160 kJ mol(-1)). The donor properties of the individual isomers of PhobPBu were assessed from the following spectroscopic measurements: (i) (1)J(PSe) for PhobP(Se)Bu; (ii) nu(CO) for trans-[RhCl(CO)(PhobPBu)(2)], (iii) (1)J(PtP) for the PEt(3) in trans-[PtCl(2)(PEt(3))(PhobPBu)]. In each case, the data are consistent with the order of sigma-donation being a(7)-PhobPBu > s-PhobPBu > a(5)-PhobPBu. This same order was found when the affinity of the PhobPBu isomers for platinum(II) was investigated by determining the relative stabilities of [Pt(CH(3))(s-PhobPBu)(dppe)][BPh(4)], [Pt(CH(3))(a(5)-PhobPBu)(dppe)][BPh(4)], and [Pt(CH(3))(a(7)-PhobPBu)(dppe)][BPh(4)] from competition experiments. Calculations of the relative stabilities of the isomers of PhobPH, [PhobPH(2)](+), and PhobPH(BH(3)) support the conclusions drawn from the experimental results. Moreover, calculations on the frontier orbital energies of PhobPMe isomers and their binding energies to H(+), BH(3), PdCl(3)(-), and PtCl(3)(-) corroborate the experimental observation of the order of sigma-donation being a(7)-PhobPR > s-PhobPR > a(5)-PhobPR. The calculated He(8) steric parameter shows that the bulk of the isomers increases in the order a(7)-PhobPR < s-PhobPR < a(5)-PhobPR. The crystal structures of [a-PhobP(CH(2)OH)(2)][s-PhobP(CH(2)OH)(2)]Cl(2), cis-[PtCl(2)(a(5)-PhobPCH(2)OH)(2)], trans-[PtCl(2)(s-PhobPBu)(2)], and trans-[PtCl(2)(a(7)-PhobPBu)(2)] are reported.

Synthesis and use of borane and platinum(II) complexes of 3‐diphenylphosphino‐1‐ phenylphospholane (LuPhos)

“…separated from the expected product 4 by column chromatography. Phospholane boranes 4 and 5 were identified by 31 P, 13 C, and 1 H NMR, as well as mass spectral data. The 31 P NMR spectrum of 4 comprised two broad signals, whereas that of 5 showed a broad signal for the ring P and a doublet of 29.9 Hz for the exocyclic P-function.…”

“…Heterocyclic P-ligands occurring in Pt(II) complexes, comprise, among others [6][7][8], arylphospholes [9,10], phospholenes [11], phospholanes [11,12], phosphinine (phosphorine) derivatives [11,12], phosphepanes [12], as well as 9-phosphabicyclononanes (Phobanes) [13] and 6-phospha-2,4,8-trioxaadamantanes [14].…”

Mixed Isobutylphobane/N‐Heterocyclic Carbene Ruthenium‐ Indenylidene Complexes: Synthesis and Catalytic Evaluation in Olefin Metathesis Reactions

“…As a matter of fact, tricyclohexylphosphane is slightly more bulky than isobutylphobane, as expressed by the Tolman cone angle (q = 1708 for PCy 3 [58] and 1638 for i-BuPhob [59] ). For nonobvious reasons, it is also a better electron donor, as measured from the values of n(CO) in trans-[RhCl(CO)A C H T U N G T R E N N U N G (PR 3 ) 2 ] complexes (1943 cm À1 for PCy 3 [60] vs. 1950 cm À1 for i-BuPhob [61] ).…”

A study on the optical resolution of 1-isopropyl-3-methyl-3-phospholene 1-oxide and its use in the synthesis of borane and platinum complexes

“…Prigle et al reported the synthesis of the platinum complexes of several 5-, 6-and 7-membered P-heterocycles [33,34]. Gouygou et al synthesized a few bisphosphole platinum-complexes [35].…”