Reactions of Coordinated Ligands. Part 19: 1 Template Synthesis of a Macrocyclic Secondary Tetraphosphine by Oxidative Demetallation of Crown Phosphine Ni(II) Complexes

Synthesis and Characterization of Phosphorus-Containing Isocyclam Macrocycles and Their Nickel Complexes

The tetradentate azamacrocycle cyclam (=1,4,8,11-tetraazacyclotetradecane) was studied profoundly for the coordination of transition metal ions, and the resulting complexes were investigated extensively for their catalytic performance in, e.g., O₂ activation and electrocatalytic CO₂ reduction. Although the successful synthesis of analogous P₄ macrocycles was described earlier, no tetradentate N,P mixed 14-membered macrocycles have been prepared to date and their chemistry remains elusive. Thus, in this work, we showcase the synthesis of phospha-aza mixed cyclam-based macrocycles by selectively "exchanging" one or two secondary amines in the macrocycle isocyclam (=1,4,7,11-tetraazacyclotetradecane) with tertiary phosphines. In addition, we herein present the preparation of the corresponding nickel complexes along with their complex chemical and structural characterization to provide first coordination studies.

Small molecule activation by POC(sp3)OP-nickel complexes

This contribution describes the reactivities of CO2 , CO, O2 , and ArNC with the pincer-type complexes [(κ(P) ,κ(C) ,κ(P') -POC sp 3OP)NiX] (POC sp 3OP=(R2 POCH2 )2 CH; R=iPr; X=OSiMe3 , NArH; Ar=2,6-iPr2 C6 H3 ). Reaction of the amido derivative with CO2 and CO leads to a simple insertion into the NiN bond to give stable carbamate and carbamoyl derivatives, respectively, the pincer ligand backbone remaining intact in both cases. In contrast, the analogous reactions with the siloxide derivative produced kinetically labile insertion products that either revert to the starting material (in the case of CO2 ) or react further to give the mixed-valent, dinickel species [(POC sp 3OP)Ni(II) {μ,κ(O) ,κ(P) ,κ(P') -OCOCH(CH2 CH2 OPR2 )2 }Ni(0) (CO)2 ]. The zero-valent center in the latter compound is ligated by a new ligand arising from transformation of the POC sp 3OP ligand backbone. The carbonylation and carboxylation of the siloxido derivative also produced minor quantities of a side-product identified as the trinickel species, [{(η(3) -allyl)Ni(μ(O) ,κ(P) -R2 PO)2 }2 Ni], arising from total dismantling of the POC sp 3OP ligand. Similar reactivities were observed with isonitrile, ArNC: reaction with the siloxido derivative resulted in a complex sequence of steps involving initial insertion, a 1,3-hydrogen shift, and an Arbuzov rearrangement to give [Ni(CNAr)4 ] and a methacrylamide based on fragments of the POC sp 3OP ligand. Oxygenation of the amido and siloxido derivatives led to the phosphinate derivative, [(POC sp 3OP)Ni(OP(O)R2 )], arising from oxidative transformation of the original ligand frame; the reaction with the Ni-NHAr derivative also gave ArHNP(O)R2 through a complex NP bond-forming reaction.

Template synthesis of benzannulated triphosphacyclononanes—a new class of phosphacrowns via template assisted nucleophilic P–C bond formation

A 9-membered triphosphorus macrocycle with o-phenylene backbone functions has been stereoselectively prepared on a CpFe(+) template by two successive nucleophilic attacks of coordinated phosphide on a coordinated o-fluorophenylbiphosphine.

Template Synthesis of 1,4,7-Triphosphacyclononanes

Iron(II) templates based on a [(eta(5)-Cp(R))Fe]+ core have been employed for the successful synthesis of 1,4,7-triphosphacyclononane derivatives (9-aneP3R'3) from a range of appropriately functionalized coordinated diphosphines and monophosphines. 1,2-Diphosphinoethane (1,2-dpe) or (2-phosphinoethyl)phenylphosphine (Phdpe) undergo a base-catalyzed Michael-type addition to trivinylphosphine, divinyl(benzyl)phosphine, or divinyl(phenyl)phosphine in [(eta(5)-Cp(R))Fe(diphosphine)(monophosphine)]+ complexes (2a-j) to give [(eta(5)-Cp(R))Fe(9aneP3R'3)]+ derivatives (4a-j) containing coordinated triphosphacyclononanes bearing one (with Phdpe) or two (with 1,2-dpe) secondary phosphine donors. The rates of macrocyclization show a dependence on the nature of the substituent(s) R on the cyclopentadienyl ligand with increased rates being observed along the series R = H5 < (Me3Si)H4 < 1,3-(Me3Si)2H3 approximately = Me5. For coupling reactions with trivinylphosphine, a pendant vinyl function remains in the macrocyclic product (4a-g) which is readily hydrogenated to the corresponding ethyl derivatives (5a-g). Further functionalization of coordinated secondary phosphines in the initially formed macrocycles (5a-g) is achieved by proton abstraction followed by addition of the appropriate alkyl halide electrophile and gives rise to tritertiary-triphospha-cyclononanes (7a-g, 7l, 7m). All new complexes have been fully characterized by spectroscopic and analytical methods in addition to the structural determination by single-crystal X-ray techniques of [{eta(5)-(Me3Si)2C5H3)Fe(9-aneP3H2C2H3)]PF6, 4c, and [(eta(5)-Me3SiC5H4)Fe(9-aneP3Et3)]BF4, 7b. 1,4,7-Triethyl-1,4,7-triphosphacyclononane is released from its metal template (7a, 7b) by treatment with either H2O2 or Br2/H2O to give the trioxide 9-aneP3(O)3Et3 (8). Attempts to recover the trivalent phosphorus species, 1,4,7-triethyl-1,4,7-triphosphacyclononane, from the trioxide by reduction proved unsuccessful.