Electrocatalytic reduction of aryldichlorophosphines with the (2,2′-bipyridine)nickel complexes

Abstract

The reduction of aryldichlorophosphines in organic solvents was studied by cyclic voltammetry, preparative electrolysis, and chemical reduction. The reaction of the electro chemically generated (2,2´ bipyridine)nickel(0) complexes with aryldichlorophosphines PhPCl 2 and tippPCl 2 (tipp is 2,4,6 triisopropylphenyl) proceeds through the formation of highly reac tive organophosphorus intermediates, whose reactions with diphenylacetylene and hex 1 ene afford phosphirene and phosphirane heterocycles, respectively.The search for new highly efficient synthetic methods is one of the principal trends of the chemistry of organo metallic and organophosphorus compounds. 1 The forma tion of element-carbon bonds, especially phospho rus-carbon bond, is an important goal of the modern organoelement chemistry. 2,3 In this context, special at tention is given to the development of novel approaches to the target synthesis of chemical compounds from highly reactive organophosphorus intermediates. Examples of such intermediates are derivatives of low coordinate phos phorus, viz., phosphinidenes [RP:] (phosphorus analogs of carbenes), which play a significant role in the synthesis of earlier unknown organophosphorus and heterocyclic compounds. 3-5 In preparative synthesis these short lived species are used, as a rule, as transition metal complexes. Presently the main and most appropriate method for their generation is the thermal decomposition of the corre sponding tungsten and molybdenum 7 phosphanorborna diene complexes. 6 Many publications are focused to the direct synthesis of various stable metal phosphinidene complexes 7,8 and investigation of their reactivity toward various organic and organoelement compounds. 8,9 Recently discovered reactions of metal phosphinidene species of the new type related to the phosphinidene group transfer from the metal center attracted attention of researchers to the practical use of the nickel complexes in organic and organophos phorus synthesis 9-11 and made it possible to improve the methods for synthesis of biologically active compounds and useful ligands. An alternative method using the [R-P-W(CO) 5 ] intermediates (R = Ar, Alk) and in cluding the step of subsequent demetallation of the ob tained organophosphorus product 4,5,12 is less convenient.A possibility of the direct synthesis of free phosphiranes and phosphirenes has been demonstrated for the first time using as an example the relatively stable nickelphosphin idene complex 9 containing the sterically hindered ligand and the substituent at the phosphorus atom. 10,11 How ever, the synthesis of this complex is difficult and consists of several steps: the formation of primary phosphine [(dtbpe)Ni(P(H)dmp)] (dtbpe is 1,2 bis(di tert butyl phosphino)ethane, and dmp is 2,6 dimesitylphenyl), its subsequent oxidation with tropilium hexafluorophosphate, and further deprotonation with NaN(SiMe 3 ) 2 . 9 Thus, this method is more complicated than the known method for synthesis of phosphanorbornadiene, which prevents its wide propagation in the synt...

Electron transfer in organonickel complexes of α-diimines: Versatile redox catalysts for C–C or C–P coupling reactions – A review

“…4) as well as from increasing reversibility of the E 1 process upon addition of excess n-Bu 4 NBr. The EC mechanism was also the conclusion from the preparative electrochemistry described above [28,32,33] and has been established for a number of diimine complexes of other transition metals such as Ru, Os, Rh, Ir or Re with halide co-ligands [18b,42-44], and also for related phosphine complexes of Pd and Ni [4,25,45] .…”

“…nickel r-aryl complexes [Ni(Ar)Br(bpy)]. A number of such complexes have been prepared independently either by electrochemical means [28,32,33] or by chemical methods (see Scheme 4, reaction A) [34][35][36][37]. In this latter case also other a-diimine ligands were introduced and the complexes were submitted to detailed studies of their electrochemical properties using electrochemical and spectroelectrochemical (UV-vis-NIR and EPR) methods [38].…”

“…This fits well into the observation that upon 4e À -reduction of [NiBr 2 (bpy)] in the presence of 2 equiv. of MesBr the dimesityl complex is obtained in high yields [28,33]. Very probably the formal Ni(I)-Ni(I) dimer complex decomposes to [Ni(II)(Mes) 2 (bpy)] and [Ni(0)(bpy)] and the latter is not stable under these conditions.…”

“…reaction as depicted in Fig. 3 was carried out with a number of substrates RX (R = aryl or alkyl) under limiting conditions [28,33]. As a result, the following sequence of substrate reactivity (k 0 -rate constants for the oxidative addition) was derived from kinetic data: MesBr < nBuBr < 2-TolBr < PhBr < 2-Cl-thiophene < PhI < i-C 5 H 11 I < i-C 3 H 7 I.…”

Preparation of Dithienylphospholes by 1,1‐Carboboration

“…We generated the lithiated thienylacetylide reagent 1 a by treatment of 2‐ethynylthiophene with n ‐butyllithium. 2,4,6‐Triisopropylphenyl phosphorus dihalide (halide=Cl, Br, for details see the Supporting Information)14 was then reacted with a slight excess (2.3 molar equivalents) of 1 a (2 h, 0 °C). Workup gave arylbis(alkynyl)phosphane 2 a as a brownish solid in 65 % yield (Scheme ).…”