The photoelectron spectrum and conformation of phenylphosphine and phenylarsine

Abstract

He(I) and He(II) photoelectron spectra of phenylphosphine and phenylarsine have been investigated and assigned. The rotational barrier of the phosphino group has been investigated at the MP2/6-31G(d,p)//MP2/6-3 IG(d,p) and HF/6-31G(d,p)//HF/6-3 IG(d,p) levels of theory, and that of the arsino group at the HF/6-3 IG(d,p)//6-31G(d,p) levels of theory. The rotational barrier of the two molecules is nearly the same. The energy difference between the two possible conformers of the molecules is low (1.5 kJ/mol at the MP2/6-31G(d,p) level of theory), allowing nearly free rotation about the P--C bond. The photoelectron spectrum cannot be interpreted by considering the most stable rotamer, but all possible conformers should be taken into account. The present interpretation is consistent with the small np-r interaction concluded from other investigations. The rotational barrier of o-phosphinophenol is significantly larger than for phenylphosphine, and the photoelectron spectrum of this compound can be interpreted by considering a single conformer, and no appreciable interaction between the r-system of the ring and the phosphorus lone pair.

π‐Excess σ2P=C–N–Heterocycles: Catalytic P‐Arylation and Alkylation of N‐Alkyl‐1,3‐benzazaphospholes and Isolation of P,N‐Disubstituted Dihydrobenzaza­phosphole P‐Oxides

“…In contrast to the diagonally related indoles, however, the reaction occurred only in the 3-position, that is, at phosphorus (Scheme 1). With water-containing disodium phosphate dodecahydrate, however, the intermediates were not detectable, which suggests that they react with moisture to the more stable final product, phosphine oxide 3a (δ = 38.2 ppm) ( [14][15][16][17]. In the presence of CsOAc but in the absence of the catalyst metal, no conversion was observed at room temperature, whereas prolonged heating at 125°C also led to slow phenylation at phosphorus (Table 1, entries 4-6).…”

“…[15] Therefore, P-arylation or alkylation of phosphinines to λ 5 -phosphinines is accomplished by the addition of RMgX or RLi reagents and subsequent treatment with alkyl halides or C 2 Cl 6 for λ 5 -P(R,X) derivatives. [14] The π-excess of the 1H-1,3-benzazaphospholes, provided by delocalization of the lone pair of electrons of the σ 3 N-atom in conjugation to phosphorus and associated with the absence of P-N bonds, raises the energy of the lone pair of electrons on P (IP v = 9.71 eV) [16] relative to that of phosphinine (IP v 10.0 eV). [17] However, the increase in the nucleophilic properties is low and the 1H-1,3-benzazaphospholes still remain passive towards methyl iodide [18] and, as shown here, also towards aryl iodides.…”

“…), DMF (4 mL), and m-iodobromobenzene (0.37 mL, 2.90 mmol) was placed in a dry Schlenk tube, heated as described above, and worked up by extraction with an equal mixture of dry n-hexane (13), P-C(21) 1.8392 (13), P-C(31) 1.8407 (13), N-C(2) 1.4386 (16), N-C(12) 1.3609 (16); C(31)-P-C(1) 99.83(6), C(2)-N-C (12) 117.70(11), N-C(12)-O 125.34 (12); C i -P-C iЈ -C oЈ (ca. ), DMF (4 mL), and m-iodobromobenzene (0.37 mL, 2.90 mmol) was placed in a dry Schlenk tube, heated as described above, and worked up by extraction with an equal mixture of dry n-hexane (13), P-C(21) 1.8392 (13), P-C(31) 1.8407 (13), N-C(2) 1.4386 (16), N-C(12) 1.3609 (16); C(31)-P-C(1) 99.83(6), C(2)-N-C (12) 117.70(11), N-C(12)-O 125.34 (12); C i -P-C iЈ -C oЈ (ca.…”

The Primary Phosphine Renaissance

“…In principle this effect could be between the phosphorus lone pair and the aromatic system, or simply within the aromatic system itself, or both. In considering this, we take into account the following: (1) conjugation of the phosphino group and aromatic rings has been a most contentious issue in the literature [15,[46][47][48][49]; (2) both 1-naphthyl and 2-naphthyl substitution lead to a similar stabilization, whereas a conjugative effect to the lone pair might be expected to show a difference; (3) there appears to be no simple relationship between the basicity of the phosphine (as defined in terms of its effect on transition metal-bound carbonyls) and its airstability, which would again imply that the phosphorus 'lone pair' is not involved in the factors imparting the air-stability; (4) a higher oxidation potential of the phosphine seems to correlate with greater air-stability; (5) PES studies [46][47][48] have To understand this issue in more detail we have undertaken molecular modeling studies of many relevant primary phosphines [50]. The geometry optimizations of each of the phosphines were performed in the gas phase at the DFT level of theory using the B3LYP functional with a 6-31G * basis set, as employed in the Spartan '06 Essential edition from Wavefunction, Inc.…”

A Non-Karplus Effect: Evidence from Phosphorus Heterocycles and DFT Calculations of the Dependence of Vicinal Phosphorus–Hydrogen NMR Coupling Constants on Lone-Pair Conformation

“…While some interaction might be possible in phosphines, with the apparent exception of vinylphosphine where the most stable structure appears to arise due to π-lone pair overlap, 61 the effect is small for the more diffuse phosphorus lone pair compared to that of nitrogen. 59,62,63 Examination of Figure 7 suggests that the phenyl rings in 6c 1 and 6c 2 are orthogonal to each other, with the phenyl approximately eclipsing the putative lone pair (and hence minimizing any π-interaction) in 6c 1 , and approximately lying orthogonal to the lone pair (and hence maximizing any π-interaction) in 6c 2 . The coupling constants differ by ~1 Hz (Table 1), but interpretation of whether this is consistent or not with differing π-interactions is complicated by the facts that both are optimized structures and so have different PNCH dihedral angles, and the phenyl ring geometries relative to the lone pair are only approximately as described.…”