Structural diversity of mixed polypnictogen complexes: dicationic E2E'2 (E ≠ E' = P, As, Sb, Bi) chains, cycles and cages stabilized by transition metals.

The reactivity of the tetrahedral dipnictogen complexes [{CpMo(CO)2}2(µ,η2:η2-EE')] (E, E' = P, As, Sb, Bi; "Mo2EE'") towards different one-electron oxidation agents is reported. Oxidation with [Thia][TEF] (Thia+ = C12H8S2 +; TEF- = Al{OC(CF3)3}4 -) leads to the selective formation of the radical monocations [Mo2EE']˙+, which immediately dimerize to the unprecedented dicationic E2E'2 ligand complexes [{CpMo(CO)2}4(µ4,η2:η2:η2:η2-E'EEE')]2+ via E-E bond formation. Single crystal X-ray diffraction revealed that, in the case of Mo2PAs and Mo2PSb, P-P bond formation occurs yielding zigzag E2P2 (E = As (1), Sb (2)) chains, whereas Mo2SbBi forms a Sb2Bi2 (5) cage, Mo2AsSb an unprecedented As2Sb2 unit representing an intermediate stage between a chain- and a cage-type structure, and Mo2AsBi a novel planar As2Bi2 (4a) cycle. Therefore, 1-5 bear the first substituent-free, dicationic hetero-E4 ligands, stabilized by transition metal fragments. Furthermore, in the case of Mo2AsSb, the exchange of the counterion causes changes in the molecular structure yielding an unusual, cyclic As2Sb2 ligand. The experimental results are corroborated by DFT calculations.

Synthesis of Tetrahedranes Containing the Unique Bridging Hetero-Dipnictogen Ligand EE' (E ≠ E'=P, As, Sb, Bi).

In order to improve and extend the rare class of tetrahedral mixed main group transition metal compounds, a new synthetic route for the complexes [{CpMo(CO)2 }2 (µ,η2 :η2 -PE)] (E=As (1), Sb (2)) is described leading to higher yields and a decrease in reaction steps. Via this route, also the so far unknown heavier analogues containing AsSb (3 a), AsBi (4) and SbBi (5) ligands, respectively, are accessible. Single crystal X-ray diffraction experiments and DFT calculations reveal that they represent very rare examples of compounds comprising covalent bonds between two different heavy pnictogen atoms, which show multiple bond character and are stabilised without any organic substituents. A simple one-pot reaction of [CpMo(CO)2 ]2 with ME(SiMe3 )2 (M=Li, K; E=P, As, Sb, Bi) and the subsequent addition of PCl3 , AsCl3 , SbCl3 or BiCl3 , respectively, give the complexes 1-5. This synthesis is also transferable to the already known homo-dipnictogen complexes [{CpMo(CO)2 }2 (µ,η2 :η2 -E2 )] (E=P, As, Sb, Bi) resulting in higher yields comparable to those in the literature reported procedures and allows the introduction of the bulkier and better soluble Cp' (Cp'=tert butylcyclopentadienyl) ligand.

Synthesis of Unprecedented 4d/4f-Polypnictogens.

A series of 4d/4f-polyarsenides, -polyarsines and -polystibines was obtained by reduction of the Mo-pnictide precursor complexes [{Cpt Mo(CO)2 }2 (µ,η2:2 -E2 )] (E=As, Sb; Cpt =tBu substituted cyclopentadienyl) with two different divalent samarocenes [Cp*2 Sm] and [(CpMe4nPr )2 Sm]. For the reductive conversion of the Mo-stibide only one product was isolated, featuring a planar tetrastibacyclobutadiene moiety as an unprecedented ligand for organometallic compounds. For the corresponding Mo-arsenide a tetraarsacyclobutadiene and a second species with a side-on coordinated As2 2- anion was isolated. The latter can be considered as reaction intermediate for the formation of the tetraarsacyclobutadiene.

Cationic Functionalisation by Phosphenium Ion Insertion.

The reaction of [Cp'''Ni(η3 -P3 )] (1) with in situ generated phosphenium ions [RR'P]+ yields the unprecedented polyphosphorus cations of the type [Cp'''Ni(η3 -P4 R2 )][X] (R=Ph (2 a), Mes (2 b), Cy (2 c), 2,2'-biphen (2 d), Me (2 e); [X]- =[OTf]- , [SbF6 ]- , [GaCl4 ]- , [BArF ]- , [TEF]- ) and [Cp'''Ni(η3 -P4 RCl)][TEF] (R=Ph (2 f), tBu (2 g)). In the reaction of 1 with [Br2 P]+ , an analogous compound is observed only as an intermediate and the final product is an unexpected dinuclear complex [{Cp'''Ni}2 (µ,η3 :η1 :η1 -P4 Br3 )][TEF] (3 a). A similar product [{Cp'''Ni}2 (µ,η3 :η1 :η1 -P4 (2,2'-biphen)Cl)][GaCl4 ] (3 b) is obtained, when 2 d[GaCl4 ] is kept in solution for prolonged times. Although the central structural motif of 2 a-g consists of a "butterfly-like" folded P4 ring attached to a {Cp'''Ni} fragment, the structures of 3 a and 3 b exhibit a unique asymmetrically substituted and distorted P4 chain stabilised by two {Cp'''Ni} fragments. Additional DFT calculations shed light on the reaction pathway for the formation of 2 a-2 g and the bonding situation in 3 a.

Triple the fun: tris(ferrocenyl)arene-based gold(i) complexes for redox-switchable catalysis.

The modular syntheses of C 3-symmetric tris(ferrocenyl)arene-based tris-phosphanes and their homotrinuclear gold(i) complexes are reported. Choosing the arene core allows fine-tuning of the exact oxidation potentials and thus tailoring of the electrochemical response. The tris[chloridogold(i)] complexes were investigated in the catalytic ring-closing isomerisation of N-(2-propyn-1-yl)benzamide, showing cooperative behaviour vs. a mononuclear chloridogold(i) complex. Adding one, two, or three equivalents of 1,1'-diacetylferrocenium[tetrakis(perfluoro-tert-butoxy)aluminate] as an oxidant during the catalytic reaction (in situ) resulted in a distinct, stepwise influence on the resulting catalytic rates. Isolation of the oxidised species is possible, and using them as (pre-)catalysts (ex situ oxidation) confirmed the activity trend. Proving the intactness of the P-Au-Cl motif during oxidation, the tri-oxidised benzene-based complex has been structurally characterised.

The Triple-Decker Complex [Cp*Fe(µ,η5:η5-P5)Mo(CO)3] as a Building Block in Coordination Chemistry.

Although the triple-decker complex [Cp*Fe(µ,η5:η5-P5)Mo(CO)3] (2) was first reported 26 years ago, its reactivity has not yet been explored. Herein, we report a new high-yielding synthesis of 2 and the isolation of its new polymorph (2'). In addition, we study its reactivity towards AgI and CuI ions. The reaction of 2 with Ag[BF4] selectively produces the coordination compound [Ag{Cp*Fe(µ,η5:η5-P5)Mo(CO)3}2][BF4] (3). Its reaction with Ag[TEF] and Cu[TEF] ([TEF]- = [Al{OC(CF3)3}4]-) leads to the selective formation of the complexes [Ag{Cp*Fe(µ,η5:η5-P5)Mo(CO)3}2][TEF] (4) and [Cu{Cp*Fe(µ,η5:η5-P5)Mo(CO)3}2][TEF] (5), respectively. The X-ray structures of compounds 3⁻5 each show an MI ion (MI = AgI, CuI) bridged by two P atoms from two triple-decker complexes (2). Additionally, four short MI···CO distances (two to each triple-decker complex 2) participate in stabilizing the coordination sphere of the MI ion. Evidently, the X-ray structure for compound 3 shows a weak interaction of the AgI ion with one fluorine atom of the counterion [BF4]-. Such an Ag···F interaction does not exist for compound 4. These findings demonstrate the possibility of using triple-decker complex 2 as a ligand in coordination chemistry and opening a new perspective in the field of supramolecular chemistry of transition metal compounds with phosphorus-rich complexes.

Dicationic E4 Chains (E=P, As, Sb, Bi) Embedded in the Coordination Sphere of Transition Metals.

The oxidation chemistry of the complexes [{CpMo(CO)2 }2 (µ,η2 :η2 -E2 )] (E=P (A), As (B), Sb (C), Bi (D)) is compared. The oxidation of A-D with [Thia]+ (=[C12 H8 S2 ]+ ) results in the selective formation of the dicationic E4 complexes [{CpMo(CO)2 }4 (µ4 ,η2 :η2 :η2 :η2 -E4 )]2+ (E=P (1), As (2), Sb (3), Bi (4)), stabilized by four [CpMo(CO)2 ] fragments. The formation of the corresponding monocations [A]+ , [C]+ , and [D]+ could not be detected by cyclic voltammetry, EPR, or NMR spectroscopy. This finding suggests that dimerization is fast and that there is no dissociation in solution, which was also predicted by DFT calculations. However, EPR measurements of 2 confirmed the presence of small amounts of the radical cation [B]+ in solution. Single-crystal X-ray diffraction revealed that the products 1 and 2 feature a zigzag E4 chain in the solid state while 3 and 4 bear a central E4 cage with a distorted "butterfly-like" geometry. Additionally, 1 can be easily and reversibly converted into a symmetric and an unsymmetric form.

Strategies for the Construction of Supramolecular Dimers versus Homoleptic 1D Coordination Polymers Starting from the Diphosphorus [Cp2Mo2(CO)4(η2-P2)] Complex and Silver(I) Salts.

The reactions of the tetrahedral diphosphorus [Cp2Mo2(CO)4(η2-P2)] (1; Cp = C5H5) complex with Ag[Al{OC(CF3)3}4] (AgTEF) (A) and Ag[FAl{OC(C6F5)(C6F10)}3] (AgFAl) (B) were studied. The first reaction led to the formation of the [Ag2(η2-1)2(η1:η1-1)2][TEF]2 (2) dimer and the [Ag2(η1:η1-1)3] n [TEF]2n (3) coordination polymer, whereas the second reaction afforded the [Ag2(η1:η1-1)2(η1-CH2Cl2)2(η2-C7H8)2][FAl]2 (4) or the [Ag2(η2-1)2(η1:η1-1)2][FAl]2 (5) dimer and the [Ag2(η1:η1-1)4] n [FAl]2n (6) coordination polymer. In each case, the products obtained depended on the ratio of the reactants and/or the synthetic procedure.

Self-Assembly of Reactive Linear Cu3 Building Blocks for Supramolecular Coordination Chemistry and Their Reactivity toward E(n) Ligand Complexes.

This study describes the selective synthesis of linear, trinuclear, halide-bridged Cu(I) complexes [Cu3(µ-X)2(µ-dpmp)2(MeCN)2](+) (1a: X = Cl; 1b: X = Br; 1c: X = I) stabilized by the tridentate dpmp ligand obtained by self-assembly reactions in THF/MeCN. Upon drying, the MeCN ligands can be removed and the complexes are transformed to the reactive parent trinuclear [Cu3(µ-X)2(µ-dpmp)2](+) (2a-c) building blocks with two vacant coordination sites on the terminal Cu atoms. Another synthesis in CH2Cl2 directly yields 2a-c. Additionally, two related isomeric compounds, 2a* and 2c*, and two CH2Cl2-ligated complexes, [Cu3(µ-X)2(µ-dpmp)2(CH2Cl2)2](+) (X = Br (3b), I (3c)), were structurally characterized. The frameworks of the cationic [Cu3(µ-X)2(µ-dpmp)2](+) complexes are stable in solution at low temperatures and show dynamic coordination behavior at elevated temperatures, indicated by new signals arising in the (31)P{(1)H} NMR spectra. This evolution cannot be shifted back by decreasing the temperature again. However, cationic [Cu3(µ-X)2(µ-dpmp)2](+) (X = Cl, Br, I) complexes can be obtained selectively in the solid state upon crystallization. Although reactions of 2a-c with complexes [{CpMo(CO)2}2(µ,η(2):η(2)-E2)] (E = P (A1), As (A2)) led to unsymmetrically substituted [Cu3(µ-X)2(µ-dpmp)2(η(1)-L)](+) (4a-c: X = Cl-I, L = A1; 5: X = Cl, L = A2) complexes, reactions with the cyclo-P3 complex [CpMo(CO)2(η(3)-P3)] (B) afforded zigzag chain polymers [Cu3(µ-X)2(µ-dpmp)2(µ,η(1):η(1)-B)]n[BF4]n (6a: X = Cl; 6b: X = Br) and symmetrically substituted complex [Cu3(µ-I)2(µ-dpmp)2(η(1)-B)2](+) (7). Reactions of 2a-c with cyclo-E5 complexes [Cp*Fe(η(5)-E5)] (E = P (C1), As (C2)) led to the isolation of one-dimensional coordination polymers [Cu3(µ-X)2(µ-dpmp)2(µ,η(1):η(1)-L)]n[BF4]n (8a-b: X = Cl-Br, L = C1; 9: X = Cl, L = C2) and symmetrically substituted complex [Cu3(µ-I)2(µ-dpmp)2(η(1)-C1)2](+) (10). All products exhibit a trinuclear, cationic [Cu3(µ-X)2(µ-dpmp)2](+) complex as the central structural motif. Variation of the intramolecular Cu-Cu distances inside the Cu3 complexes is discussed, and supporting DFT computations for the model complex [Cu3(µ-Cl)2(dmmp)2{(η(1)-A1)}](+) (4a') are presented.

Organometallic polyphosphorus and -arsenic ligands as linkers between pre-assembled linear Cu(I) fragments.

A simple and straightforward synthesis of a new linear trinuclear Cu(I) cluster with polyphosphine ligands is presented. The reaction of this pre-organized Cu3 precursor with En ligand complexes (E = P, As; n = 2, 5) affords discrete complexes exhibiting end-on η(1)-coordination of the E2 ligands or one-dimensional coordination polymers featuring σ-1,3-bridging E5 rings, respectively.