Reactions of cyclonickelated complexes with hydroxylamines and TEMPO˙: isolation of new TEMPOH adducts of Ni(II) and their reactivities with nucleophiles and oxidants.

This contribution describes a study on the reactivities of the complexes [{κP,κC-(i-Pr)2PO-Ar}Ni(µ-Br)]2, 1a-d (Ar: C6H4, a; 3-Cl-C6H3, b; 3-OMe-C6H3, c; 4-OMe-napthalenyl, d), with hydroxylamines in the presence of TEMPO˙ (TEMPO˙ = (2,2,6,6-tetramethylpiperidinyl-1-yl)oxyl). The results of this study showed that treating 1a-d with a mixture of Et2NOH and TEMPO˙ did not afford the desired oxidation-induced functionalization of the Ni-aryl moiety in 1a-d, giving instead the corresponding κO-TEMPOH adducts [{κP,κC-(i-Pr)2PO-Ar}Ni(Br)(κO-TEMPOH)], 3a-d (TEMPOH = N-hydroxy-2,2,6,6-tetramethylpiperidine). The TEMPOH moiety in these zwitterionic compounds 3 can be displaced by a large excess of acetonitrile (MeCN), 10 equiv. of morpholine, or 1-2 equivalents of imidazole. Although these reactions have given the authenticated products [{κP,κC-(i-Pr)2PO-C6H4}Ni(Br)(NCMe)], 4a, [{κP,κC-(i-Pr)2PO-C6H4}Ni(Br)(morpholine)], 5a, and [{κP,κC-(i-Pr)2PO-C6H4}Ni(imidazole)2]Br, 6a, a few other products were also detected by NMR, indicating that the observed reactivities are far more complex than simple substitution of the TEMPOH moiety. Similarly, treating 3a with AgOC(O)CF3 results in the isolation of [{κP,κC-(i-Pr)2PO-C6H4}Ni{OC(O)CF3}(κO-TEMPOH)], 7a, arising from the substitution of the bromo ligand, whereas spectroscopic evidence suggests further reactivity, possibly including displacement of TEMPOH and oxidative decomposition.

Correction: In vitro and in vivo antiproliferative activity of organo-nickel SCS-pincer complexes on estrogen responsive MCF7 and MC4L2 breast cancer cells. Effects of amine fragment substitutions on BSA binding and cytotoxicity.

Correction for 'In vitro and in vivo antiproliferative activity of organo-nickel SCS-pincer complexes on estrogen responsive MCF7 and MC4L2 breast cancer cells. Effects of amine fragment substitutions on BSA binding and cytotoxicity' by Mahboubeh Hosseini-Kharat et al., Dalton Trans., 2018, 47, 16944-16957, https://doi.org/10.1039/c8dt03079k.

Reactivities of cyclonickellated complexes with hydroxylamines: formation of κO-hydroxylamine and κN-imine adducts and a κO, κN-aminoxide derivative.

This report discusses the reactivities of hydroxylamines with a family of nickellacyclic complexes prepared by C-H nickellation of aryl phosphinites. Treating the dimeric complexes κC,κP-{2-OPR2,4-R'-C6H4}2Ni2(µ-Br)2 (R = i-Pr; R' = H, Cl, OMe, NMe2) or their monomeric acetonitrile adducts κC,κP-{2-OPR2,4-R'-C6H4}Ni(Br)(NCMe) with hydroxylamines showed three types of reactivities depending on the Ni complex, the reaction solvent, and the substrate used: (1) the benzyl-protected substrate PhCH2ONH2 gave simple N-bound adducts with all Ni complexes; (2) the parent Ni dimer (R' = H) reacted with Et2NOH and (PhCH2)2NOH in CH2Cl2 to give, respectively, the zwitterionic amine oxide κC,κP-{2-OPR2-C6H5}Ni(κO-ONHEt2)Br and the bidentate aminoxide (i-R2POPh)Ni{κO,κN-ON(CH2Ph)2}Br; (3) the analogous reaction of substituted Ni complexes (R' = Cl, OMe, NMe2) with hydroxylamines in acetonitrile gave adducts of imines derived from dehydration of Et2NOH and (PhCH2)2NOH. The latter reactivity proceeds optimally in acetonitrile, but it also occurs to a lesser extent in C6D6 if the reaction is allowed to go for more than 24 h. Different mechanistic scenarios have been considered to rationalize the observed hydroxylamine → imine transformation.

Cytotoxicity, anti-tumor effects and structure-activity relationships of nickel and palladium S,C,S pincer complexes against double and triple-positive and triple-negative breast cancer (TNBC) cells.

Triple-Negative Breast Cancer (TNBC) is a highly aggressive form of breast cancer. The high rate of metastasis associated with TNBC is attributed to its multidrug resistance, making the treatment of this metastatic condition difficult. The development of metal-based antitumor agents was launched with the discovery of cisplatin, followed by the development of related antitumor drugs such as carboplatin and oxaliplatin. Yet, the severe side effects of this approach represent a limitation for its clinical use. The current search for new metal-based antitumor agents possessing less severe side effects than these platinum-based complexes has focused on various complexes of nickel and palladium, the group 10 congeners of platinum. In this work, we have prepared a series of SCS-type pincer complexes of nickel and palladium featuring a stable meta-phenylene central moiety and two chelating but labile thioamide donor moieties at the peripheries of the ligand. We have demonstrated that the complexes in question, namely L1NiCl, L1NiBr, L1PdCl, L2PdCl, and L3PdCl, are active on the proliferation of estrogen-dependent breast tumor cells (MCF-7 and MC4L2) and triple-negative breast cancer (4 T1). Among the complexes studied, the palladium derivatives were found to be much safer anticancer agents than nickel counterparts; these were thus selected for further investigations for their effects on tumor cell adhesion and migration as well. The results of our studies show that palladium complexes are effective for inhibiting TNBC 4 T1 cells adhesion and migration. Finally, the HOMO and LUMO analysis was used to determine the reactivity and charge transfer within the compounds.

Correction: C-H nickellation of phenol-derived phosphinites: regioselectivity and structures of cyclonickellated complexes.

Correction for 'C-H nickellation of phenol-derived phosphinites: regioselectivity and structures of cyclonickellated complexes' by Loïc P. Mangin et al., Dalton Trans., 2017, 46, 16159-16170, DOI: 10.1039/C7DT03403B.

C-O and C-N Functionalization of Cationic, NCN-Type Pincer Complexes of Trivalent Nickel: Mechanism, Selectivity, and Kinetic Isotope Effect.

This report presents the synthesis of new mono- and dicationic NCN-NiIII complexes and describes their reactivities with protic substrates. (NCN is the pincer-type ligand κ N, κ C, κ N-2,6-(CH2NMe2)2-C6H3.) Treating van Koten's trivalent complex (NCN)NiIIIBr2 with AgSbF6 in acetonitrile gives the dicationic complex [(NCN)NiIII(MeCN)3]2+, whereas the latter complex undergoes a ligand-exchange reaction with (NCN)NiIIIBr2 to furnish the related monocationic complex [(NCN)NiIII(Br)(MeCN)]+. These trivalent complexes have been characterized by X-ray diffraction analysis and EPR spectroscopy. Treating these trivalent complexes with methanol and methylamine led, respectively, to C-OCH3 or C-NH(CH3) functionalization of the Ni-aryl moiety in these complexes, C-heteroatom bond formation taking place at the ipso-C. These reactions also generate the cationic divalent complex [(NCN)NiII(NCMe)]+, which was prepared independently and characterized fully. The unanticipated formation of the latter divalent species suggested a comproportionation side reaction between the cationic trivalent precursors and a monovalent species generated at the C-O and C-N bond formation steps; this scenario was supported by direct reaction of the trivalent complexes with the monovalent compound (PPh3)3NiICl. Kinetic measurements and density functional theory analysis have been used to investigate the mechanism of these C-O and C-N functionalization reactions and to rationalize the observed inverse kinetic isotope effect in the reaction of [(NCN)NiIII(Br)(MeCN)]+ with CH3OH/CD3OD.

Antiproliferative activity of morpholine-based compounds on MCF-7 breast cancer, colon carcinoma C26, and normal fibroblast NIH-3T3 cell lines and study of their binding affinity to calf thymus-DNA and bovine serum albumin.

This report describes the results of a study on the antiproliferative activity of the morpholine-based ligand 1,3-bis(1-morpholinothiocarbonyl)benzene (HL) and its nickel(II) complex (NiL) against human breast cancer cells (MCF-7), colon carcinoma cells (C26), and normal fibroblast NIH-3T3 cells. NiL showed better cytotoxicity on both cancerous cells relative to normal cells in vitro with the highest selective index of 2.22 in MCF-7 cells. The interaction of both compounds with calf thymus DNA (CT DNA) and bovine serum albumin (BSA) was studied using various spectroscopic techniques and analytical methods such as UV - vis titrations, thermal denaturation, circular dichroism, competitive fluorescent intercalator displacement assays, as well as molecular modeling. The fluorescence intensity of the probe molecule increases clearly when HL and NiL are added to the methylene blue (MB)-DNA system. Furthermore, the binding of HL and NiL quenches the BSA fluorescence, revealing a 1:1 interaction with a binding constant of about 105 M-1. Communicated by Ramaswamy H. Sarma.

In vitro and in vivo antiproliferative activity of organo-nickel SCS-pincer complexes on estrogen responsive MCF7 and MC4L2 breast cancer cells. Effects of amine fragment substitutions on BSA binding and cytotoxicity.

A family of organonickel complexes has been prepared, fully characterized, and tested for their antiproliferative activity against estrogen-responsive human breast cancer cells (MCF7). The three SCS-type pincer ligands HL1, HL2, and HL3 and their corresponding Ni(ii) complexes NiL1, NiL2, and NiL3 have been synthesized and fully characterized, including by single crystal diffraction studies for the complexes. The complexes possess square planar geometry with two symmetrical 5-membered nickellacycles. Fluorescence spectroscopy, circular dichroism measurements, molecular modeling, colorimetric based assay and tumor transplantation studies were used to evaluate the protein binding and antiproliferative activities of these organometallic complexes both in vitro and in vivo. Fluorescence quenching was used to investigate bovine serum albumin (BSA) interaction at different temperatures (293, 303 and 313 K), and the results were analyzed using the classical Stern-Volmer equation, allowing us to propose a dynamic quenching mechanism. Studies in vitro on the antiproliferative activity of the three organonickel complexes against estrogen-responsive human breast cancer cells (MCF7) showed promising antitumor activity for NiL1 containing pyrrolidine fragments. In vivo administration of this compound significantly inhibits tumor growth in estrogen-dependent MC4L2 cancer cells in female BALB/c mice.

C-H nickellation of phenol-derived phosphinites: regioselectivity and structures of cyclonickellated complexes.

This report describes the results of a study on the ortho-C-H nickellation of the aryl phosphinites i-Pr2P(OAr) derived from the following four groups of substituted phenols: 3-R-C6H4OH (R = F (b), Me (c), MeO (d), Cl (e)); 3,5-R2-C6H3OH (R = F (f), Me (g), Cl (h), OMe (i)); 2-R-C6H4OH (R = Me (j), Ph(k)); and 2,6-R2-C6H3OH (R = Me (l), Ph (m)). No nickellation was observed with the phosphinites derived from the 3,5-disubstituted phenols g and h, and the 2,6-disubstituted phenols l and m; in all other cases nickellation occurred at an ortho-C-H to generate either the Br-bridged dimers [{κP,κC-(i-Pr)2POAr}Ni(µ-Br)]2 (1b-1f, 1j, and 1k) or the monomeric acetonitrile adduct {κP,κC-ArOP(i-Pr)2}Ni(Br)(NCMe) (1i-NCMe). Analysis of C-H nickellation regioselectivity with 3-R-C6H4OH pointed to the importance of substituent sterics, not electronics: nickellation occurred at the least hindered position either exclusively (for R = Me (c), MeO(d), and Cl (e)) or predominantly (for R = F (b); 6 : 1). This conclusion is also consistent with the observation that C-H nickellation is possible with the 3,5-disubstituted aryl phosphinites bearing F and OMe, but not with the more bulky substituents Me or Cl. For the 2-substituted aryl phosphinites, C-H nickellation occurs at the unsubstituted ortho-C-H and not on the R substituent, regardless of whether the alternative C-H moiety of the substituent is sp3 (R = Me (j)) or sp2 (R = Ph (k)). The system thus reveals a strong preference for formation of 5-membered metallacycles. Consistent with this reactivity, no nickellation occurs with (2,6-R2-C6H3O)P(i-Pr)2. Tests with the parent dimer derived from i-Pr2P(OPh) showed that conversion to the monomeric acetonitrile adduct is highly favored, going to completion with only a small excess of MeCN. All new cyclonickellated complexes reported in this study were fully characterized, including by single crystal X-ray diffraction studies. The solid state structures of the dimers 1b and 1d showed an unexpected feature: two halves of the dimers displayed non-coplanar conformations that place the two Ni(ii) centers at shortened distances from each other (2.94-3.16 Å). Geometry optimization studies using DFT have shown that such non-coplanar conformations stabilize the complex, implying that the "bending" observed in these complexes is not caused by packing forces. Indeed, it appears that the occurrence of coplanar conformations in the solid state structures of these dimers is a simple consequence of packing forces rather than an intrinsic property of the compound.

Manganese-mediated synthesis of an NHC core non-symmetric pincer ligand and evaluation of its coordination properties.

The alkylation of N-(2-pyridyl)imidazole by the MnI methylene-phosphonium complex [Cp(CO)2Mn(η2-P,C-Ph2P[double bond, length as m-dash]C(H)Ph)]BF4 offers a straightforward route to a tridentate pro-ligand featuring an NHC core and phosphine/pyridine arms. The ability of this PCN ligand to coordinate in a pincer mode was recognized in RhI, RhIII, and NiII complexes.

Reactions of Phenylhydrosilanes with Pincer-Nickel Complexes: Evidence for New Si-O and Si-C Bond Formation Pathways.

This contribution presents evidence for new pathways manifested in the reactions of the phenylhydrosilanes PhnSiH4-n with the pincer complexes (POCsp(2)OP)Ni(OSiMe3), 1-OSiMe3, and (POCsp(3)OP)Ni(OSiMe3), 2-OSiMe3 (POCsp(2)OP = 2,6-(i-Pr2PO)2C6H3; POCsp(3)OP = (i-Pr2POCH2)2CH). Excess PhSiH3 or Ph2SiH2 reacted with 1-OSiMe3 to eliminate the disilyl ethers Ph(n)H(3-n)SiOSiMe3 (n = 1 or 2) and generate the nickel hydride species 1-H. Subsequent reaction of the latter with more substrate formed corresponding nickel silyl species 1-SiPhH2 or 1-SiPh2H and generated multiple Si-containing products, including disilanes and redistribution products. The reaction of 1-OSiMe3 with excess Ph2SiH2/Ph2SiD2 revealed a net KIE of ca. 1.3-1.4 at room temperature. Treating 1-OSiMe3 with excess Ph3SiH also gave 1-H and the corresponding disilyl ether Ph3SiOSiMe3, but this reaction also generated the new siloxide 1-OSiPh3 apparently via an unconventional σ-bond metathesis pathway in which the Ni center is not involved directly. The reaction of excess PhSiH3 and 2-OSiMe3 gave polysilanes of varying solubilities and molecular weights; NMR investigations showed that these polymers arise from Ni(0) species generated in situ from the reductive elimination of the highly reactive hydride intermediate, 2-H. The stoichiometric reactions of 2-OSiMe3 with Ph2SiH2 and Ph3SiH gave, respectively, siloxides 2-OSiPh2(OSiMe3) and 2-OSiPh3. Together, these results demonstrate the strong influence of pincer backbone and hydrosilane sterics on the different reactivities of 1-OSiMe3 and 2-OSiMe3 toward Ph(n)SiH(4-n) (dimerization, polymerization, and redistribution vs formation of new siloxides). The mechanisms of the reactions that lead to the observed Si-O, Si-C, and Si-Si bond formations are discussed in terms of classical and unconventional σ-bond metathesis pathways.

Charge Effects in PCP Pincer Complexes of Ni(II) bearing Phosphinite and Imidazol(i)ophosphine Coordinating Jaws: From Synthesis to Catalysis through Bonding Analysis.

This contribution reports on a new family of Ni(II) pincer complexes featuring phosphinite and functional imidazolyl arms. The proligands (R) PIMC(H) OP(R') react at room temperature with Ni(II) precursors to give the corresponding complexes [((R) PIMCOP(R') )NiBr], where (R) PIMCOP(R) =κ(P) ,κ(C) ,κ(P) -{2-(R'2 PO),6-(R2 PC3 H2 N2 )C6 H3 }, R=iPr, R'=iPr (3 b, 84 %) or Ph (3 c, 45 %). Selective N-methylation of the imidazole imine moiety in 3 b by MeOTf (OTf=OSO2 CF3 ) gave the corresponding imidazoliophosphine [((iPr) PIMIOCOP(iPr) )NiBr][OTf], 4 b, in 89 % yield ((iPr) PIMIOCOP(iPr) =κ(P) ,κ(C) ,κ(P) -{2-(iPr2 PO),6-(iPr2 PC4 H5 N2 )C6 H3 }). Treating 4 b with NaOEt led to the NHC derivative [(NHCCOP(iPr) )NiBr], 5 b, in 47 % yield (NHCCOP(iPr) =κ(P) ,κ(C) ,κ(C) -{2-(iPr2 PO),6-(C4 H5 N2 )C6 H3 )}). The bromo derivatives 3-5 were then treated with AgOTf in acetonitrile to give the corresponding cationic species [((R) PIMCOP(R) )Ni(MeCN)][OTf] [R=Ph, 6 a (89 %) or iPr, 6 b (90 %)], [((R) PIMIOCOP(R) )Ni(MeCN)][OTf]2 [R=Ph, 7 a (79 %) or iPr, 7 b (88 %)], and [(NHCCOP(R) )Ni(MeCN)][OTf] [R=Ph, 8 a (85 %) or iPr, 8 b (84 %)]. All new complexes have been characterized by NMR and IR spectroscopy, whereas 3 b, 3 c, 5 b, 6 b, and 8 a were also subjected to X-ray diffraction studies. The acetonitrile adducts 6-8 were further studied by using various theoretical analysis tools. In the presence of excess nitrile and amine, the cationic acetonitrile adducts 6-8 catalyze hydroamination of nitriles to give unsymmetrical amidines with catalytic turnover numbers of up to 95.

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.

On the stability of a POCsp3OP-type pincer ligand in nickel(II) complexes.

We describe the results of a study on the stabilities of pincer-type nickel complexes relevant to catalytic hydroalkoxylation and hydroamination of olefins, C-C and C-X couplings, and fluorination of alkyl halides. Complexes [(POCsp3 OP)NiX] are stable for X=OSiMe3 , OMes (Mes=1,3,5-Me3 C6 H2), NPh2, and CC-H, whereas the O(tBu) and N(SiMe3)2 derivatives decompose readily. The phenylacetylide derivative transforms gradually into the zero-valent species cis-[{κ(P),κ(C),κ(C')-(iPr2 POCH2 CHCH2 )}Ni{η(2),κ(C),κ(C')-(iPr2 P(O)CCPh)}]. Likewise, attempts to prepare [(POCsp3 OP)NiF] gave instead the zwitterionic trinuclear species [{(η(3) -allyl)Ni}2-{µ,κ(P),κ(O)-(iPr2 PO)4 Ni}]. Characterization of these two complexes provides concrete examples of decomposition processes that can dismantle POCsp3 OP-type pincer ligands by facile C-O bond rupture. These results serve as a cautionary tale for the inherent structural fragility of pincer systems bearing phosphinite donor moieties, and provide guidelines on how to design more robust analogues.

Antitumor, antioxidant and antimicrobial studies of substituted pyridylguanidines.

A series of N-pivaloyl-N'-(alkyl/aryl)-N''-pyridylguanidine of general formula C4H9CONHC(NR¹R²)NPy have been synthesized and characterized using elemental analysis, FT-IR, multinuclear NMR spectroscopy, and in the case of compounds 7 and 11, by single crystal X-ray diffraction (XRD). The synthesized guanidines were tested for antitumor activities against potato tumor, and showed excellent inhibition against Agrobacterium tumefaciens (AT10)-induced tumor. The antioxidant and antimicrobial activities of these new compounds against various bacterial and fungal strains were also investigated.

P(CH)P pincer rhodium(I) complexes: the key role of electron-poor imidazoliophosphine extremities.

The coordination chemistry of a potentially pincer-type dicationic meta-phenylene-bis(imidazoliophosphine) ligand 3 to neutral and cationic carbonylrhodium(I) centers has been investigated. Similarly to what was observed previously for its ortho-phenylene counterpart, 3 was found to bind to the RhCl(CO) fragment in a trans-chelating manner that makes possible a weak Rh-C(H) interaction, inferred from the nonbonding but relatively short Rh-C and Rh-H contacts observed in the solid state structure of the dicationic adduct (3)RhCl(CO) (5). Formation of the target PCP-type pincer complex could not be triggered despite multiple attempts to deprotonate the central C-H moiety in the initial dicationic adduct 5, or in the tricationic species [(3)Rh(CO)](+) (8) generated by abstraction of the chloride ion from 5. Complex 8 was identified on the basis of NMR and IR analyses as a Rh(I)-stabilized P(CH)P-intermediate en route to the anticipated classical PCP-type pincer complex. Analysis of the electronic structure of this intermediate computed at the density functional level of theory (DFT level) revealed a bonding overlap between a Rh d-orbital and π-orbitals of the m-phenylene ring. NBO analyses and calculated Wiberg indices confirm that this interaction comprises an η(1)-C-Rh bonding mode, with only secondary contributions from the geminal C and H atoms. Although the target PCP-type pincer complex could not be generated, treatment of the tricationic intermediate with methanol induced a P-CN(2) bond cleavage at both imidazoliophosphine moieties, resulting in the formation of a dicationic "open pincer" species, that is, a nonchelated bis((MeO)PPh(2))-stabilized aryl-Rhodium complex that is the κC-only analogue of the putative κP,κC,κP-PCP complex sought initially. Theoretical studies at the DFT level of experimental or putative species relevant to the final C-H activation process ruled out the oxidative addition pathway. Two alternative pathways are proposed to explain the formation of the "open pincer" complex, one based on an organometallic α-elimination step, the other based on an organic aromatization-driven ß-elimination process.

Nickel(II) complexes of the new pincer-type unsymmetrical ligands PIMCOP, PIMIOCOP, and NHCCOP: versatile binding motifs.

Chelation/nickellation of an unsymmetrical meta-phenylene-based ligand featuring phosphinite and imidazolophosphine functionalities gives the corresponding pincer complex. N-Methylation of the latter generates a new complex featuring the ternary moiety NHC→Ph(2)P(+)→Ni, which can be converted subsequently into the binary moiety NHC→Ni by extrusion of Ph(2)P(+), thus allowing a sequential synthesis of pincer complexes displaying varying degrees of dipolar character.

[2,6-Bis(diphenyl-phosphan-yloxy)phenyl-κP,C,P']hydroxidonickel(II).

The mol-ecule of the title complex, [Ni(C(30)H(23)O(2)P(2))(OH)], adopts a slightly distorted square-planar geometry around Ni(II) defined by the coordination of the two mutually trans P atoms, the Csp(2) atom of the pincer ligand and the O atom of the hydroxide ligand. The largest distortions from ideal geometry are reflected in the smaller than usual P-Ni-P [163.95 (3)°] and P-Ni-C [82.06 (6)°] angles. The OH ligand does not form intra- or inter-molecular hydrogen bonds.

{2,6-Bis[(diphenyl-phosphan-yl)-oxy]phen-yl-κP,C,P'}iodidonickel(II).

In the title complex, [Ni(C(30)H(23)O(2)P(2))I], the divalent Ni atom is coordinated by two P atoms and one C atom from the 1,3-bis-[(diphenyl-phosphan-yl)-oxy]benzene ligand; the distorted square-planar geometry is completed by an iodide ligand. The largest distortions from ideal square-planar geometry are reflected in the P-Ni-P angle of 164.20 (2)° and the P-Ni-C angles of 82.09 (6) and 82.11 (6)°. The rather short Ni-C bond length [1.890 (2) Å] is anti-cipated in light of the much stronger trans influence of the aryl moiety compared to the iodide ligand. The P-bound phenyl rings adopt different orientations to minimize steric repulsion among themselves.