A rearrangement of 1,1-linked four-membered rings to bicyclic bridgehead five-membered rings: A phosphorus turn

Abstract

Novel rearrangements of 2,3,2',3'-tetra-tert-butyl-4,4'-bis-trimethylsilanyloxy-1,2,1',2'-tetrahydro-[1,1']biphosphetyl (7) to 1,2,5,6-tetra-tert-butyl-3,7-bis-trimethylsilanyloxy-1H,5H-[1,2]diphospholo-[1,2-a][1,2]diphosphole (9) and of 3,4,3,4-tetra-tert-butyl-[1,1']biphosphetanyl-2,2'-dione (10) to 2,3,6,7-tetra-tert-butyl-tetrahydro-[1,2]diphospholo[1,2-a][1,2]diphosphole-1,5-dione (12) were observed during sublimation at 150 degrees C in 0.1 mm vacuum. The C-P-C internal angles of the four-membered rings, which reflect steric strain in (7), were 71.9(2) degrees and 77.9(1) degrees; the C-P-P internal angles of the five-membered rings of 9 were 90.88(6) degrees and 93.02(6) degrees after rearrangement. Reaction of 7 with metallic caesium provided the caesium salt of 3,4-di-tert-butyl-3,4-dihydro-phosphet-2-ol (15), which is the first example of a 2lambda-3-phospha-1-enolate being incorporated into four-membered ring. Due to its large size, the caesium cation has a rare coordination mode with both the phosphorus and oxygen atoms of the 2lambda-3-phospha-1-enolate, forming infinite polymeric chains in the solid state of 15. Two tert-butyl groups in the vicinal positions of compounds 7, 9, 10, 12 and 15 dictate the gauche conformations in compounds 7, 9, 10, 12 and 15, enforcing this stereoselectivity around the C-C-C portion of the rings in the enlargement reaction.

Highly unsaturated phosphorus compounds: Trimeric and dimeric sulfides of a α,β‐di‐tert‐butyl vinyl phosphaalkyne

“…Formally, compound 10 can be considered as a dimerization product of intermediate phosphalkyne sulfide 9 with two additional hydrogen abstractions probably from the solvent. The similar rearrangements and plausible mechanisms have been reported by us for analogous tervalent phosphorus systems, which have a tendency to form stable five‐membered bridgehead bicyclic rings, e.g., compound 11 9.…”

Reactivity Studies on a Diazadiphosphapentalene

“…[7] For diphosphapentalene derivatives that possesst wo phosphorus(III) atoms at the bridgehead, [8] four major ring systems III-VI have been structurally characterized ( Figure 1b). [9][10][11][12] However,s tudies on their reactivities have been limited to the coordinationn atures towards transition metals, [8b, 11g, 12] their oxidation, [8a, 11 f, 12] and reaction with Grignardr eagents, [10a-c] and thus still remainu nexplored. Considering the importance of phosphorus heterocycles, both the development of unique molecular frameworks and ad eep comprehension of their reactivities are essential to broadening their diversity from afundamental point of view.…”

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

“…The doublet for the phosphaalkene carbon atom in the four‐membered ring appears at δ =244.6 ppm ( 1 J (P,C)=75.7 Hz) in the 13 C{ 1 H} NMR spectrum. This is downfield shifted of the respective signals in five‐membered heterocycles with a phosphoruscarbon double bond ( δ =211–213 ppm)20 and still downfield shifted from a four‐membered heterocycle with a phosphoruscarbon double bond ( δ =234.9 ppm, 1 J (P,C)=41.2 Hz) 21. These analyses clearly showed that a [2+2] cycloaddition and concomitant TMSCl elimination occurred.…”

“…The significantly smaller O1‐Si1‐P1 angle in compound 5 compared with compound 6 (77.60(7) and 77.60(6)° vs. 112.2(2)°, respectively) is likely due to the different coordination number of the silicon atom (five in compound 5 and four in compound 6 ). The angle on the phosphorus atom is comparable to another four‐membered ring with a CP bond (C‐P‐C 76.9(1)°) 21. The t Bu group on the carbon atom is bent toward the oxygen atom and thus away from the phosphorus atom (C17‐C16‐P1: 130.5(2) and 131.1(2)° vs. C17‐C16‐O1: 115.6(2) and 115.2(2)°), which was previously observed for another PCO heterocycle (C‐C‐P: 131.75(14)° vs. C‐C‐O: 113.4(2)°) 20a…”

“…The siliconphosphorus bond length of 2.2384(10) and 2.2414(9) Å is in the range of a siliconphosphorus single bond (compare 2.2838(12) Å in compound 1 and 2.095(3) Å in compound 2 )5a and longer than in other four‐membered rings with siliconphosphorus bonds (2.1894(7) and 2.2012(7) Å in LSi‐P‐SiL‐C(Ad), and 2.1737(6) and 2.1742(6) Å in (LSiP) 2 ) 22. The carbon–phosphorus double bond of 1.732(3) and 1.733(3) Å in compound 5 is in the range of other phosphorus–carbon double bonds in heterocycles (1.699(2), 1.705(1), 1.729(3), and 1.755(2) Å)20, 21 and longer than the average carbon–phosphorus bond length in acyclic phosphaalkenes (average: 1.67 Å, range 1.63–1.80 Å) 23…”