The synthesis of N-heterocyclic carbene-diphosphine macrocycles by metal template assisted cyclization reactions has been explored. Attempts to prepare the facial tungsten tricarbonyl precursor complex containing an NH,NH-functionalized carbene and a suitable diphosphine resulted in displacement of the coordinated carbene and the isolation of the corresponding diphosphine tungsten tetracarbonyl [3]. The Re(I) chloro tetracarbonyl complex bearing an NH,NH-functionalized carbene ligand [5] can be prepared and is a suitable precursor for the subsequent formation of the carbene-diphosphine tricarbonyl intermediate [H(2)-6]Cl bearing reactive 2-fluoro substituents at the phosphine-phenyl groups. Two of these fluoro substituents are displaced by a nucleophilic attack upon deprotonation of the coordinated NH,NH-functionalized carbene resulting in new C-N bonds resulting in the partially coupled intermediate, [10], followed by the desired complex with the macrocyclic ligand [8]Cl. Compounds [H-7]Cl and [8]Cl are also formed during the synthesis of [H(2)-6]Cl as a result of spontaneous HF elimination. Complex [8](+) may be converted to the neutral dicarbonyl chloro analog [11] by action of Me(3)NO. Related chemistry with analogous manganese complexes is observed. Thus, from the NH,NH-functionalized carbene manganese bromo tetracarbonyl [12], the diphosphine manganese carbene tricarbonyl cation [H(2)-13] may be readily prepared which provides the macrocyclic carbene-diphosphine tricarbonyl cation [14](+) following base promoted nucleophilic intramolecular displacement of fluoride. Again, [14](+) is converted to the neutral bromo dicarbonyl upon reaction with Me(3)NO. All complexes with the exception of the reaction intermediate [10] have been characterized by spectroscopic and analytical methods in addition to X-ray crystallographic structure determinations for complexes [3], [5], [H(2)-6]Cl, [H(2)-6][9], [8]Cl, [10], [11], [12], and [14]Br.

carbenes · carbodicarbenes · carbodiphosphoranes · divalent carbonIsitpossibletocoordinatetwodonorligandsLtoacarbon (0) atom, and what would be the properties of such a carbon atom? These questions have been of interest to chemists for many years. First answers to this question have been obtained with the synthesis [1] and structural characterization [2] of carbodiphosphoranes (CDPs) A using donor ligands of type L = R 3 P.[3] Carbodiphosphoranes can be formulated as bisphosphine complexes of a naked carbon atom (Aa). Alternatively, a heterocumulene R 3 P=C=PR 3 (Ab) resonance structure and the description as a carbenoid species (Ac) are possible. The bonding parameters and reactivity of the carbodiphosphoranes indicate that the electronic situation of these compounds is reasonably described by a polar structure with two electron lone pairs at the central carbon atom (Aa, Scheme 1).The related carbodiarsoranes [4] as well as a series of cyclic carbodiphosphoranes [2f, 5] have also been described. Carbodiphosphoranes are all strong bases and nucleophiles. The high degree of charge excess at the ylidic carbon atom, which is not compensated by the phosphorus centers, makes them good donor ligands. The electronic situation found in carbodiphosphoranes differs however from that in diphosphino-or diaminocarbenes. A comparison of cyclic derivatives of these three types of donor ligands (Scheme 2) illustrates these differences. The carbene carbon atoms of N-heterocylic carbenes (NHCs) [6] or P-heterocyclic carbenes (PHCs)

Rhenium complex []Cl with the coordinated [11]ane-P(2)C(NHC) macrocycle was obtained by a metal template controlled ring formation reaction; in this reaction a coordinated NH,NH-stabilised imidazolidin-2-ylidene ligand was connected via the nitrogen atoms to two phenyl substituents of a 2-fluorophenyl substituted diphosphine ligand.

No abstract

Starting from complexes of type [Ru(Cp)Cl(P-P)] (P-P = 2PPh3, 3a; P-P = 2PMe3, 3b: P-P = dppe, 3c; P-P = dppp, 3d) isocyanide complexes [Ru(Cp)(P-P)(CNR) 4a-4d (CNR = CN-CH2-CH2N3, 1) and 7a-7d (CN-C6H4-2N3, 2) have been prepared. Reduction of the azido functions of the coordinated isocyanide ligands with Zn/NH4Cl/H2O in methanol leads to coordinated 2-amino functionalized isocyanides which cyclize to yield the complexes with a saturated NH,NH-stabilized NHC ligand 5a-5d or a benzannulated NH,NH-stabilized NHC ligand 8a-8d. The Zn/NH4Cl/H2O reduction method is of general applicability and allowed the generation of complex 11 bearing three saturated NH,NH-stabilized NHC ligands.