Isomerization, Ring Expansion, and Ring Contraction of 1,3‐Diphosphete Complexes

Abstract

Reactions between the 1,3-diphosphete complex [Cp'''Co(η -P C tBu )] (1) and Ag[Al{OC(CF ) } ] (Ag[pftb]) were carried out under different conditions. In CH Cl , the unprecedented 1,2-diphosphete isomerization product [Ag {Cp'''Co(μ,η :η :η -1,2-P C tBu )} {Cp'''Co(μ,η :η -1,2-P C tBu )} ]⋅2[pftb] (2) could be isolated. In diffusion experiments of 1 in n-hexane with Ag[pftb] in CH Cl , the triphosphacobaltocenium complex [Cp'''Co(η -P C tBu )][pftb] (4) and the phosphirenylium complex [Cp'''Co(η -PC tBu )][pftb] (5) were obtained, showing a ring expansion and a ring contraction, respectively, under mild conditions. Moreover, addition of pyridine to the Ag complex 2 led to the new 1,2-diphosphete complex [Cp'''Co(η -1,2-P C tBu )] (3). Compound 3 is also formed by thermolysis of 1, making it a promising method for this type of isomerization. 1,2-Diphosphete complexes like 3 are thermodynamically more stable but also synthetically more elusive than their 1,3-isomer counterparts.

Flexidentate Coordination Behavior and Chemical Non‐Innocence of a Bis(1,3‐Diphosphacyclobutadiene) Sandwich Anion

“…The hydrogen atoms are omitted for clarity.Thermal ellipsoids are drawn at the 50 %p robability level. Selectedb ond lengths []a nd angles [8]f or 2:Ni1ÀP1 2.1807(8), P1ÀC1 1.784(3),P 1 ÀC2 1.785(3), P2ÀC1 1.800(3),P2 ÀC2 1.799(3), P1C1P2C2/ P3C3P4C4 6.09; 3:Ni1ÀCo1 2.536(1), Ni1ÀP1 2.179(2), Ni1ÀC1 1.902 (7), P1ÀC2 1.770 (7), C2ÀP2 1.754 (7),P 2 ÀC1 1.783 (6), P1-Ni1-C1 94.6(2), Ni1-C1-P2 116.3(3), P1C1P2C2/ P3C3P4C4 12.48; 4:Ni1ÀCo1 2.5447 (7), Ni1ÀP1 2.144 (1),N i1ÀP2 2.1568(9), P1ÀC1 1.798(3), P2ÀC2 1.795(3), C1ÀC2 1.447(4), P2-Ni1-P1 88.54(3), Ni1-P1-C1 110.0(1), C2-P2-Ni1 110.0(1), NiP1C1P2C2/ P3C3P4C4 13.73. b] displayed four signals for the chemically inequivalent tert-butyl substituents at d = 0.83, 1.08, 1.46, and 1.79 ppm, and as inglet at d = 5.31 ppm for the Cp ligand.…”

“…The cyclic voltammogram of 5 (THF/[nBu 4 N]PF 6 ,F igure S42, Supporting Information) features two reversible redox events at E1 = 2 = À0.46 and À2.10 V( vs. Fc/Fc + + ), which may tentatively be assigned to the reversible oxidation and reduction of the complex, respectively.T he cyclic voltammogram of 6 (THF/ [nBu 4 N]PF 6 ,F igure S43) shows two successive reversible oxidation waves at E1 = 2 = À0.63 and 0.00 V( vs. Fc/Fc + + ). It is noteworthy that anions of type A show only one reversible oxidation event (E1 = 2 = À0.73 Vv s. Fc/Fc + for [K( [18]crown-6)(thf) 2 {Co(P 2 C 2 tBu 2 ) 2 }]).…”

“…The most remarkable feature of the molecular structure of 10 is the presenceo fa1 ,4-diphospha-2-butene ligand, which has rarely been observed so far (see Figure 3a bove for the related complex G reported by Binger andc o-workers). The P1ÀP2 distance of 2.401(1) ,t hat is, approximately 0.2 longer than in known 1,2-diphosphacyclobutadiene complexes, [6] indicates that the PÀPb ond is weakened, and the structure of 10 thus may be viewed as ap roduct of an arrested PÀPb ond addition onto palladium. The P1ÀP2 distance of 2.401(1) ,t hat is, approximately 0.2 longer than in known 1,2-diphosphacyclobutadiene complexes, [6] indicates that the PÀPb ond is weakened, and the structure of 10 thus may be viewed as ap roduct of an arrested PÀPb ond addition onto palladium.…”

“…Althought he 1,2-isomer is more stable with small organic substituents, bulky groups such as R = tBu favor the formation of the 1,3isomer. [5,6] Our group developed anionic bis(1,3-diphosphacyclobutadiene) sandwich complexes [M(P 2 C 2 R 2 ) 2 ] À (M = Fe, Co;t ype A, Scheme1), [7] which were obtained from the reactiono fb is(an-thracene) metalates [M(h 4 -C 14 H 10 ) 2 ] À (M = Fe, Co;C 14 H 10 = anthracene) [8] with phosphaalkynes such as tBuÀCP, tPentÀCP, and AdÀCP( tBu = tert-butyl, tPent = tert-pentyl, Ad = adamantyl). [4] Since then, numerous 1,3diphosphacyclobutadiene complexes as well as some 1,2-diphosphacyclobutadiene complexes have been described.…”

“…[4] Since then, numerous 1,3diphosphacyclobutadiene complexes as well as some 1,2-diphosphacyclobutadiene complexes have been described. [5,6] Our group developed anionic bis (1,3-diphosphacyclobutadiene) sandwich complexes [M(P 2 C 2 R 2 ) 2 ] À (M = Fe, Co;t ype A, Scheme1), [7] which were obtained from the reactiono fb is(an-thracene) metalates [M(h 4 -C 14 H 10 ) 2 ] À (M = Fe, Co;C 14 H 10 = anthracene) [8] with phosphaalkynes such as tBuÀCP, tPentÀCP, and AdÀCP( tBu = tert-butyl, tPent = tert-pentyl, Ad = adamantyl). Four Pa toms are present in these molecules, which may potentially enable ar ich coordinationc hemistry.…”