The Conversion of Furans into Phosphinines

Abstract

The [4+2] cycloadducts between furan compounds and a methylenechlorophosphane pentacarbonyltungsten complex are converted into the corresponding 2-hydroxy- or 2-bromophosphinine complexes by treatment with BBr(3) and triethylamine. The X-ray crystal structure of the parent 2-phosphaphenol complex shows that the hydroxy substituent is coplanar with the ring and that the conjugation between the π lone pair of electrons on the oxygen atom and the ring leads to lengthening of the P-C(OH) bond. This complex is methylated at the phosphorus atom by methyl iodide with disruption of the ring aromaticity. The complex is further silylated, acylated, and triflated at the oxygen atom with retention of the aromatic structure, and decomplexation by 1,2-bis(diphenylphosphino)propane (DPPE) leads to the free parent 2-phosphaphenol. The comparison of the X-ray crystallographic structural analysis of the 2-bromophosphinine complex with an earlier structure of the analogous 2-chlorophosphinine complex suggests that 2-bromo species is a better ligand than 2-chlorophosphinine. When the [4+2] adducts are treated with BBr(3) and water, a 2-hydroxy-3-bromo-1,2,3,6-tetrahydrophosphinine derivative is obtained, which yields a seven-membered 2,1-phosphaoxepin when treated with an amine.

A Phosphorus Analogue of Acenaphthylene

“…It appears that the methoxy substitution is sufficient to provide stability. The activation of the P=C double bond by the complexation of the low‐lying phosphorus lone pair is also quite similar to what was observed in studies of 2‐phosphaphenol …”

3‐Bromo‐2‐Pyrone: An Alternative and Convenient Route to Functionalized Phosphinines

“…Due to the rather sterically demanding TMS group and the Br substituent both in α‐position of the phosphorus heterocycle, the planar aromatic ring is rotated out of the plane defined by three of the five carbonyl ligands and the phosphinine moiety (dihedral angle C(10)−W(1)−P(1)−C(5)=41.9°). A similar conformation has been observed for phosphinine complexes containing a Cr(CO) 5 or W(CO) 5 fragment …”

“…As imilar conformation has been observed for phosphininec omplexes containing aC r(CO) 5 or W(CO) 5 fragment. [17,18] The structuralc haracterizationo f20 nicely proves that the phosphinine 19 was regioselectivelyf ormed in af acile manner, (1) 1.213(11), C(1)ÀC(2) 1.451 (11), C(2)ÀC(3) 1.349 (10), C(3)ÀC(4) 1.415 (10), C(4)ÀC (5) 1.351(11), C(5)ÀO(1) 1.355(9), C(2)À Br(1)1.891 (7). www.chemeurj.org startingf rom 3-bromo-2-pyrone (16)a nd Me 3 Si-C P. This methodc an, thus, be used for the convenient synthesis of 6bromo-a nd 2-TMS-functionalized phosphinines and the overall reactionsequence is summarized in Scheme 8.…”

Electron‐Rich Aromatic 1,3‐Heterophospholes – Recent Syntheses and Impact of High Electron Density at σ2P on the Reactivity

“…The 31 P coordination chemical shifts (Δ δ ) of the benzazaphosphole complexes 59 M relative to those of the corresponding ligands ( 5a ,68 4b – d , 9b 11b,92) are small for M = Cr and show the same trends with respect to the metal as the analogous di‐ and triazaphosphole M(CO) 5 complexes 60 M ,63 61 M , and 62 M ,95 as well as the phosphinine complexes 63 M ,96 but the Δ δ values of 59 M indicate smaller net donicity, possibly through somewhat stronger backbonding towards phosphorus (Figure 5). The crystal structure analysis of the 1,5‐dimethylbenzazaphosphole complex ( 10a ) · W(CO) 5 displays small but significant deviations of the metal from the ring plane (bend angles of the W–P vector to the ring plane 7.5 and 7.8°)36 relative to those in the Cr(CO) 5 complexes of pivaloyl‐2‐phosphaindolizine (1.5°)93a and 1,5‐dimethyl‐1,2,3‐diazaphosphole (2°),95W(CO) 5 complexes of electron‐rich (+ M ) o ‐alkoxy‐ or 2‐hydroxy‐substituted phosphinines (0.7–3.3°),52b as well as to L 4 M 0 complexes (M = Pt, Ni) of P–N‐type azaphosphole ligands 98…”