New Route to Access an Acyl‐Functionalized Phosphasilene and a Four‐Membered Si‐P‐C‐O Heterocycle

Abstract

An acyl-functionalized phosphasilene, LSi(COtBu)=P(SiMe3) (L = PhC(NtBu)2) was synthesized on a new route by the addition of tBuCOCl to the phosphinosilylene LSiP(SiMe3)2 and subsequent Me3SiCl elimination. DFT studies elucidated its molecular structure, the influence of the acyl group on UV/Vis transitions, and revealed the mechanism. The intermediate LSi(COtBu)ClP(SiMe3)2, with a five-coordinate silicon center, was characterized by NMR spectroscopy and X-ray analysis. On the other hand, phosphasilene LSi(SiMe3)=P(SiMe3) reacted with tBuCOCl by a [2+2] cycloaddition of the silicon-phosphorus double bond and the carbon-oxygen double bond in addition to Me3SiCl elimination, thereby affording the novel, fully characterized compound LSi(SiMe3)[P=C(tBu)O] bearing a Si-P-C-O heterocycle with a phosphorus-carbon double bond. DFT studies suggest that two mechanisms occur simultaneously.

Advances in Phosphasilene Chemistry

“…Akin to 30 , the electronic structure of phosphasilene 31 (Figure ) with an acyl substituent at silicon displays pronounced zwitterionic character. The doubly bonded phosphorus and silicon nuclei of 31 resonate upfield to those of 30 , at δ( 31 P)=−265 ppm and δ( 29 Si)=5.0 ppm.…”

“…The doubly bonded phosphorus and silicon atoms are both significantly shielded, resonating at high field at δ( 31 P)=−252.9 ppm and δ( 29 Si)=40.5 ppm ( 1 J Si,P =191.4 Hz), indicating the presence of electron‐donation effects from the amidinate ligand and trimethylsilyl groups. DFT calculations (RI‐B97‐D/6‐31G* level of theory) supported strong polarization of the Si δ+ =P δ− π bond. NBO analysis revealed the predominant location of π‐electron density at phosphorus (78.5 %), leading to a charge separation (Si: +0.99; P: −0.75).…”

“…Phosphanylsilylene 72 readily reacts with pivaloyl chloride to afford selectively the corresponding Si ‐acylphosphasilene 31 , apparently through an intermediate formation of the adduct 73 supported by DFT calculations (more stable than 72 by 14.9 kcal mol −1 ), and following elimination of chlorotrimethylsilane (Scheme ). Single crystals of intermediate 73 were obtained from hexane at low temperature and its molecular structure was elucidated by XRD analysis.…”

Facile Access to Stable Silylium Ions Stabilized by N-Heterocyclic Imines

“…The difference in the steric bulk of the precursors 1 and 3 leads to different products based on the reaction kinetics. Figure 3 shows the energy profile along the reaction path calculated at the B97-D/6-31G(d) level of theory which has been successfully applied in low-valent silicon compounds [38][39][40][41][42][43][44][45][46][47]. The first step in the reaction is the abstraction of a Me group of a Me 3 Si moiety by the B(C 6 F 5 ) 3 (TS1 Dip ) with the associated energy of +18.9 kcal/mol for 2[MeB(C 6 F 5 ) 3 ] 2 .…”

Synthesis and Reactivity of Functionalized Silicon(II) Compounds: Iminosilylene, Phosphinosilylene, Hydrosilylene, and Related Compounds

“…Acyl-functionalized phosphasilene 34 was obtained in 41% yield as colorless solid from 1:1 stoichiometric reaction of pivaloyl chloride and freshly prepared phosphinosilylene 19 (Scheme 10). 42 The signal at δ = 236.2 ppm ( 2 J P,C = 21.3 Hz) in the 13 C{ 1 H} NMR spectrum signifies the presence of carbonyl H} NMR signal of compound 34 at δ = ¹265 ppm compared to zweitterionic phosphasilene 29 (δ = ¹253 ppm) (Scheme 7) unequivocally confirms slightly enhanced negative polarization towards phosphorus in 34. The computed structure shows distorted tetrahedral geometry around the silicon center.…”