Z-type Ligands Research Articles

Ligand Surface Chemistry Dictates Light Emission from Nanocrystals.

There are several contradictory accounts of the changes to the emissive behavior of semiconductor nanocrystal upon a ligand exchange from trioctylphosphine/cadmium-phosphonates passivation to N-butylamine. This communication explains the contradictory accounts of this reaction using new insights into ligand chemistry. Also, a previously unknown link between surface emission and cadmium-phosphonate (Z-type) ligands is shown.

ChemInform Abstract: Pentacoordination for Pincer and Related Terdentate Coordination Compounds: Revisiting Structural Properties and Trends for D8 Transition Metal Systems

AbstractReview: 116 refs.

Metal-only Lewis pairs between group 10 metals and Tl(i) or Ag(i): insights into the electronic consequences of Z-type ligand binding.

Complexes bearing electron rich transition metal centers, especially those displaying coordinative unsaturation, are well-suited to form reverse-dative σ-interactions with Lewis acids. Herein we demonstrate the generality of zerovalent, group 10 m-terphenyl isocyanide complexes to form reverse-dative σ-interactions to Tl(i) and Ag(i) centers. Structural and spectroscopic investigations of these metal-only Lewis pairs (MOLPs) has allowed insight into the electronic consequences of Lewis-acid ligation within the primary coordination sphere of a transition metal center. Treatment of the bis-isocyanide complex, Pt(CNArDipp2)2 (ArDipp2 = 2,6-(2,6-(i-Pr)2C6H3)2C6H3) with TlOTf (OTf = [O3SCF3]-) yields the Pt/Tl MOLP [TlPt(CNArDipp2)2]OTf (1). 1H NMR and IR spectroscopic studies on 1, and its Pd congener [TlPd(CNArDipp2)2]OTf (2), demonstrate that the M → Tl interaction is labile in solution. However, treatment of complexes 1 and 2 with Na[BArF4] (ArF = 3,5-(CF3)2C6H3) produces [TlPt(CNArDipp2)2]BArF4 (3) and [TlPd(CNArDipp2)2]BArF4 (4), in which Tl(i) binding is shown to be static by IR spectroscopy and, in the case of 3, 195Pt NMR spectroscopy as well. This result provides strong evidence that the M → Tl linkages can be attributed primarily to σ-donation from the group 10 metal to Tl, as loss of ionic stabilization of Tl by the triflate anion is compensated for by increasing the degree of M → Tl σ-donation. In addition, X-ray Absorption Near-Edge Spectroscopy (XANES) on the Pd/Tl and Ni/Tl MOLPs, [TlPd(CNArDipp2)2]OTf (2) and [TlNi(CNArMes2)3]OTf, respectively, is used to illustrate that the formation of a reverse-dative σ-interaction with Tl(i) does not alter the spectroscopic oxidation state of the group 10 metal. Also reported is the ability of M(CNArDipp2)2 (M = Pt, Pd) to form MOLPs with Ag(i), yielding the complexes [AgM(CNArDipp2)2]OTf (5, M = Pt; 6, M = Pd). As was determined for the Tl-containing MOLPs 1-4, it is shown that the spectroscopic oxidation states of the group 10 metal in 5 and 6 are essentially unchanged compared to the zerovalent precursors M(CNArDipp2)2. However, in the case of 5 and 6, the formation of a dative M → Ag σ-bonding interaction facilitates the binding of Lewis bases to the group 10 metal trans to Ag, illustrating the potential of acceptor fragments to open up new coordination sites on transition metal complexes without formal, two-electron oxidation.

Air-stable cationic gold(I) catalyst featuring a Z-type ligand: promoting enyne cyclizations.

An air-stable cationic Au(I) complex featuring a Z-type ligand (boron atom) as a σ-acceptor was developed for elucidating the effect of B on catalytic reactions. An enyne cyclization in the presence of either [Au→B](+) or [Au](+) showed that [Au→B](+) promotes the reactivity, which enabled the effective construction of not only five- and six-membered rings, but also seven-membered rings.

Telluroether to Telluroxide Conversion in the Coordination Sphere of a Metal: Oxidation-Induced Umpolung of a Te–Au Bond

While Ph2Te is oxidized into Ph2TeCl2 in the presence of (tht)AuCl (tht = tetrahydrothiophene), reaction of (o-(Ph2P)C6H4)2Te (LTeP2) with the same gold reagent affords the complex LTeP2AuCl (1). Upon reaction with Ph3P, this complex is converted into [LTeP2AuPPh3][Cl] ([2][Cl]). Complex 1 also reacts with H2O2 to afford the telluroxide gold chloride complex (o-(Ph2P)C6H4)2Te(═O)AuCl (3). The three new complexes have been fully characterized. Their crystal structures indicate the presence of a Te–Au bond with lengths of 2.874(4), 2.937(2), and 2.9864(5) Å, for 1, [2][Cl], and 3, respectively. Natural bond orbital analysis shows that oxidation of 1 into 3 results in an umpolung of the Te–Au bond which switches from Te→Au in 1 to Te←Au in 3. These results show that the telluroxide moiety of 3 acts as a Z-type ligand.

Redox and anion exchange chemistry of a stibine-nickel complex: writing the L, X, Z ligand alphabet with a single element.

According to the covalent bond classification (CBC) method, two-electron donors are defined as L-type ligands, one-electron donors as X-type ligands, and two-electron acceptors as Z-type ligands. These three ligand functions are usually associated to the nature of the ligating atom, with phosphine, alkyl, and borane groups being prototypical examples of L-, X- and Z-ligands, respectively. A new SbNi platform is reported in which the ligating Sb atom can assume all three CBC ligand functions. Using both experimental and computational data, it is shown that PhICl2 oxidation of (o-(Ph2P)C6H4)3SbNi(PPh3) (1) into [(o-(Ph2P)C6H4)3ClSb]NiCl (2) is accompanied by a conversion of the stibine L-type ligand of 1 into a stiboranyl X-type ligand in 2. Furthermore, the reaction of 2 with the catecholate dianion in the presence of cyclohexyl isocyanide results in the formation of [(o-(Ph2P)C6H4)3(o-O2C6H4Sb)]Ni(CNCy) (4), a complex featuring a nickel atom coordinated by a Lewis acidic, Z-type, stiborane ligand.

Ligand Exchange and the Stoichiometry of Metal Chalcogenide Nanocrystals: Spectroscopic Observation of Facile Metal-Carboxylate Displacement and Binding

We demonstrate that metal carboxylate complexes (L-M(O2CR)2, R = oleyl, tetradecyl, M = Cd, Pb) are readily displaced from carboxylate-terminated ME nanocrystals (ME = CdSe, CdS, PbSe, PbS) by various Lewis bases (L = tri-n-butylamine, tetrahydrofuran, tetradecanol, N,N-dimethyl-n-butylamine, tri-n-butylphosphine, N,N,N',N'-tetramethylbutylene-1,4-diamine, pyridine, N,N,N',N'-tetramethylethylene-1,2-diamine, n-octylamine). The relative displacement potency is measured by (1)H NMR spectroscopy and depends most strongly on geometric factors such as sterics and chelation, although also on the hard/soft match with the cadmium ion. The results suggest that ligands displace L-M(O2CR)2 by cooperatively complexing the displaced metal ion as well as the nanocrystal. Removal of up to 90% of surface-bound Cd(O2CR)2 from CdSe and CdS nanocrystals decreases the Cd/Se ratio from 1.1 ± 0.06 to 1.0 ± 0.05, broadens the 1S(e)-2S(3/2h) absorption, and decreases the photoluminescence quantum yield (PLQY) from 10% to <1% (CdSe) and from 20% to <1% (CdS). These changes are partially reversed upon rebinding of M(O2CR)2 at room temperature (∼60%) and fully reversed at elevated temperature. A model is proposed in which electron-accepting M(O2CR)2 complexes (Z-type ligands) reversibly bind to nanocrystals, leading to a range of stoichiometries for a given core size. The results demonstrate that nanocrystals lack a single chemical formula, but are instead dynamic structures with concentration-dependent compositions. The importance of these findings to the synthesis and purification of nanocrystals as well as ligand exchange reactions is discussed.

Coordination Complexes of Bismuth Triflates with Tetrahydrofuran and Diphosphine Ligands

The reaction of CH3OSO2CF3 (MeOTf) with BiBr3 in tetrahydrofuran (THF) yields (THF)2BiBr2(OTf) (1), which is converted to (dmpe)BiBr2(OTf) (2Br) upon displacement of the THF ligands with bis(dimethylphosphino)ethane (dmpe). The chloride derivatives (dmpe)BiCl2(OTf) (2Cl) and (dmpe)BiCl(OTf)2 (3) are obtained from the reaction of BiCl3 and dmpe with 1 and 2 equiv of Me3SiOSO2CF3 (TMSOTf), respectively. The complexes readily decompose in solution to give elemental bismuth and a mixture of products. The solid-state structures reveal dimeric units bridged by both triflate O-S-O interactions and weak Bi-X-Bi interactions (X = Cl, Br). Comparison of the solid-state structures illustrates that both cis and trans configurations of halides are possible in complexes of the form L2BiX2(OTf), depending upon the denticity of the ligand. The experimentally observed configurations are consistent with minima calculated at the MP2 level for the triflate-free cations in the gas phase. Examination of the MP2-calculated electronic structure of 3 reveals the presence of low-lying π-type orbitals that may result in Z-type ligand activity. However, the attempted coordination of 3 with the electron-rich metal center in K2PdCl4, via metal-to-ligand back-donation, leads instead to halide abstraction, giving [(dmpe)2Pd][(CH3CN)2Bi2Cl6(OTf)2] (8). The anion in 8 consists of two octahedral bismuth environments bridged along one edge by two triflate anions. The results illustrate new coordination chemistry for bismuth.

ChemInform Abstract: σ‐Acceptor, Z‐Type Ligands for Transition Metals

AbstractReview: 105 refs.

Chemistry of Transition Metal Complex Containing Sigma Electron Acceptor (Z-type) Ligand

In this contribution, the chemistry of borane ligands acting as sigma electron acceptors has been reviewed briefly. Borane works as a Lewis acid by its empty p orbital, and can withdraw the electron density from the transition metal through the s interaction between d orbital of transition metal and p orbital of borane. This class of borane ligand is referred to Z-type ligand, which should have a fascinating property to tune the electron density of the metal center. Recently, Peters and his co-worker have made significant contribution to the chemistry of Z-type ligand. They have isolated the series of iron complexes with the TPB ligand that span four different electronic states ranging from (Fe-B)6 to (Fe-B)9. Achievement of syntheses of these (TPB)Fe complexes having various electron configurations likely results from the ability of the Fe→B interaction to respond to changes in the electronic properties of the metal center.

σ-Acceptor, Z-type ligands for transition metals

The ability of Lewis acids to coordinate to transition metals as σ-acceptor ligands was recognized as early as in the 1970's, but so-called Z-type ligands remained curiosities until the early 2000's. Over the last decade, significant progress has been made in this area, especially via the incorporation of Lewis acid moieties into multidentate, ambiphilic ligands. Our understanding of the nature and influence of TM → Z interactions has considerably improved and the scope of Lewis acids susceptible to behave as σ-acceptor ligands has been significantly extended. This feature article summarizes these recent achievements.

Metallaboratranes Derived from a Triphosphanyl–Borane: Intrinsic C3 Symmetry Supported by a Z‐Type Ligand

Metallaboratranes Derived from a Triphosphanyl–Borane: Intrinsic <i>C</i>₃ Symmetry Supported by a Z‐Type Ligand

Metallaboratranes Derived from a Triphosphanyl–Borane: Intrinsic C3 Symmetry Supported by a Z‐Type Ligand

Metallaboratranes Derived from a Triphosphanyl–Borane: Intrinsic <i>C</i>₃ Symmetry Supported by a Z‐Type Ligand

Transition‐Metal Complexes Featuring Z‐Type Ligands: Agreement or Discrepancy between Geometry and dn Configuration?

Transition‐Metal Complexes Featuring Z‐Type Ligands: Agreement or Discrepancy between Geometry and d^<i>n</i> Configuration?

Transition‐Metal Complexes Featuring Z‐Type Ligands: Agreement or Discrepancy between Geometry and dn Configuration?

Transition‐Metal Complexes Featuring Z‐Type Ligands: Agreement or Discrepancy between Geometry and d^<i>n</i> Configuration?