Geminal frustrated Lewis pairs (FLPs) are expected to exhibit increased reactivity when the donor and acceptor sites are perfectly aligned. This is shown for reactions of the nonfluorinated FLP tBu(2)PCH(2)BPh(2) with H(2), CO(2), and isocyanates and supported computationally.
No abstract
dried. Yield: 2.75 g, 97% yield of crude air-sensitive red-orange 2-4THF. Pure 2-2DME was obtained by slow diffusion ofn-hexane into a solution of 2 dissolved in DME. C,,H,,Na,O,P, (red-orange crystals), M , = 971.01, crystal dimensions 0 . 3 2~0 . 3 2~0 . 3 2 m m . triclinic, Pi (No. 2). a=11.909(1), h=14.819(2). c=16.901(2)A. rx =95.29(1). /(=101.23(1). 7 =112.58(1)", V=2654.0 ( l ) A 3 ,Final R = 0 044, R, = 0 065 for 9550 observed unique reflections with 2OmdX = 60 having F: > 3.0n(F;). Solution by direct methods; 595 variables refined using toIFol -IF,I)' by full matrix least squares. GOF =1.19. , =1.05 A' in the final difference map [13].3: Potassium metal (0.91 g, 23.3 mmol) and tetramer 1 (4.00 g, 5.38 mmol) were heated to 70 C in freshly distilled DME (100 mL) for 12 h. The crude precipitate of air-sensitive pale yellow needles was collected, washed with DME, and dried. Yield of 3.4DME: 6.3Og. 93%. Crystals suitable for X-ray diffraction were grown by dil%sion of hexane into a THF solution containing equimolar amounts of 3 and [18]crown-6. C'(pale yellow crystals). M , = 2006.69, crystal dimensions 0.20 x 0 30 x 0.34 mm, monoclinic, P2lin (No. 14). a = 17.445(2), h = 15.783(1). c = 20 382(2) A. /( = 102.2711) . V = 5483.5(2) A3, 2 = 2, pcs,cd =1.215 gcm-3, j.(MoK.) = 0.71073 A, ) I = 2.8cm-l. F(OO0) = 2152, T = 123 k0.5 K. Final K = 0.056, R, = 0.072 for 5664 observed unique reflections with 20,,, = 60 having FZ > 3.0u(F:). Solution by direct methods; 595 variables refined using !-,(lFol -IF,[)' by full matrix least squares.. GOF =1.22. (Ap),az,m,n = 0.57 A' in the final difference map 1131.
Strain gives cyclopropane derivatives their unique electronic and chemical properties. 1 Spirofusion of three-membered rings augments the strain by 8.5 kcal/mol, 2 and yet many stable linear and branched [n]triangulanes are known, 3,4 but instead only few hetero[n]-triangulanes are known, irrespective of whether it concerns spirocyclopropanated aziridines, oxiranes, thiiranes, siliranes, or phosphiranes. 3 The higher reactivity of the heterocyclic ring is believed to be the underlying cause. In contrast, we now report on the exceptional stability of a branched phospha [7]triangulane.Reaction of carbene-like terminal phosphinidene complex [PhPdW(CO) 5 ], 5 generated in situ by cheletropic elimination from 1 at 100°C in toluene, with second-generation bicyclopropylidene 2 4 afforded W(CO) 5 -complexed phospha [7]triangulane 3 (mp 178-179°C, 88%) as the sole product (Scheme 1). Its 31 P NMR resonance at δ -119.6 is deshielded by 9.8 from the first-generation triangulane 6 and by 70.5 ppm from parent 4. 7 This illustrates little influence of the second spirocyclopropane sphere, but the larger phospha[15]triangulane could not be synthesized from thirdgeneration bicyclopropylidene 5 4 because of its too congested double bond. 4b The stabilizing W(CO) 5 group was subsequently removed from 3. While oxidation with iodine at -30°C 8 afforded [W(CO) 4 I] + I --complexed phospha [7]triangulane [δ( 31 P) -130.1], quenching with N-methylimidazole 8 only led to degradation. Instead direct ligand exchange in refluxing xylene (150°C!) with (Ph 2 PCH 2 ) 2 (dppe) 9 was more successful, giving free phospha [7]triangulane 6 (mp 168-169°C, 82%) as the sole product (Scheme 2). 10 Its δ( 31 P) at -164.0 shows the expected shielding on demetalation, and the increased 1 J(P,C) coupling from 6.2 (3) to 37.3 Hz resembles that for the parent 1-phenylphosphirane. 7,11 The molecules of 6 are located on an exact mirror plane in the crystal (Figure 1) 12 and show slightly elongated P-C and P-Ph bonds (by respectively 0.02 and 0.01 Å) due to the absence of the stabilizing W(CO) 5 group.The exceptional thermal stability of 3 and 6 is remarkable as most phosphiranes eliminate or transfer [Ph-PdW(CO) 5 ] at much lower temperatures (e100-115°C). 10 That the six spirofused rings indeed stabilize the CCP ring is evident from the mere 6.5 kcal/ mol difference in strain energies (SE), determined with homodesmotic reactions at G3(MP2), 13 between parent phospha [7]triangulane 6′ (H for Ph; 224.2 kcal/mol) and alkene 2 (217.7 kcal/mol); phosphirane C 2 PH 5 has an SE of 20.8 kcal/mol. A contributing factor is the release of olefin strain (OS) in 2 that amounts to 23.1 kcal/ mol (see Supporting Information). The higher stability of 6 is also related to a higher olefinic π-donor and π*-acceptor ability in 2 4 caused by spirocyclopropanation, which is reflected in the 9.3 kcal/ mol larger exothermicity for reaction of 1 PH (A 1 ) with 2 (82.9 kcal/mol) than for 1 PH with ethylene (73.5 kcal/mol; G3(MP2)). This behavior is in line with a higher HOMO (-8...
The synthesis of a variety of benzophosphepine complexes [R = Ph, t-Bu, Me; ML(n )()= W(CO)(5), Mo(CO)(5), Cr(CO)(5), Mn(CO)(2)Cp] by two successive hydrophosphinations of 1,2-diethynylbenzene is discussed in detail. The first hydrophosphination step proceeds at ambient temperature without additional promoters, and subsequent addition of base allows full conversion to benzophosphepines. Novel benzeno-1,4-diphosphinanes were isolated as side products. The benzophosphepine complexes themselves serve as convenient phosphinidene precursors at elevated, substituent-dependent temperatures (>55 degrees C). Kinetic and computational analyses support the proposal that the phosphepine-phosphanorcaradiene isomerization is the rate-determining step. In the absence of substrate, addition of the transient phosphinidene to another benzophosphepine molecule is observed, and addition to 1,2-diethynylbenzene furnishes a delicate bidentate diphosphirene complex.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.