Low-valent metal isocyanide complexes. III. Inversion at the nitrogen atoms of bridging isocyanide ligands

1974 ◽  
Vol 13 (2) ◽  
pp. 249-253 ◽  
Author(s):  
R. D. Adams ◽  
F. A. Cotton
Keyword(s):  
Isocyanide Ligands ◽  
Low Valent

Basen-induzierte Alkin-Spaltung in W(II)-Komplexen – ein neuer Weg zu niedervalenten Carbin-Komplexen aus W(CO)6 / Base-Induced Alkyne Cleavage in W(II) ComplexesaNew Way to Low Valent Carbyne Complexes from W(CO)6

1990 ◽  
Vol 45 (3) ◽  
pp. 351-368 ◽  
Author(s):  
Alexander Constantin Filippou ◽  
Christian Völkl ◽  
Walter Grünleitner ◽  
Paul Kiprof
Keyword(s):  
Bond Cleavage ◽  
Nucleophilic Attack ◽  
Monoclinic Space Group ◽  
High Electron ◽  
Hindered Rotation ◽  
Isocyanide Ligands ◽  
Single Transition ◽  
Low Valent ◽  
Alkyne Complexes ◽  
Carbyne Complexes

A new entry to low-valent, carbonyl-free tungsten phenylcarbyne complexes has been developed from W(CO)6 via tungsten(II) alkyne complexes. The first step includes thermal decarbonylation of W(CO)6 to fac-W(CO)3(MeCN)3 and subsequent substitution of the acetonitrile ligands by EtNC or t-BuNC to give fac-W(CO)3(EtNC)3 (1 a) or fac-W(CO)3(t-BuNC)3 (1 b) in almost quantitative yields. Advantages of this indirect synthesis of 1 a and 1 b from W(CO)6 are discussed in comparison to the previously described, CoCl2 catalyzed transformation of W(CO)6 with RNC to fac-W(CO)3(RNC)3. Compounds 1 a and 1 b are then quantitatively converted with Br2 to W(CO)2(EtNC)3(Br)2 (2 a) and W(CO)2(t-BuNC)3(Br)2 (2b). 2 a and 2b react subsequently with PhC=CBr to give upon elimination of both CO ligands the carbonylfree compounds W(EtNC)3(η2-PhC=CBr)(Br)2 (3a) and W(t-BuNC)3(η2-PhC=CBr)(Br)2 (3b) in good yield. 3 a and 3b represent rare examples of complexes containing a 1-haloalkyne ligand. They are susceptible to nucleophilic attack at this ligand. Thus reaction of 3 a and 3 b witht-BuNH2 or Et2NH gives the 1-aminoalkyne complexes W(EtNC)3[η2-PhC=CNH(t-Bu)](Br)2 (4a), W(t-BuNC)3[η2-PhC≡CNH(t-Bu)](Br)2 (4 b) and W(t-BuNC)3(η2-PhC=CNEt2)(Br)2 (4c) in good yields. Finally a base-induced cleavage of the alkyne ligand is achieved in 4 a and 4b using LiPh and gives the carbyne complexes mer,trans-Br(t-BuNC)(EtNC)3W=CPh (5a) and trans-Br(t-BuNC)4W=CPh (5b). This decoupling reaction is the first example of an alkyne-bond cleavage to C1-fragments at a single transition metal center and the key step in the new synthetic procedure to 5 a and 5 b from W(CO)6. Complex 5 b has been previously prepared from W(CO)6 by the classical Fischer route via the carbonyl containing carbyne complextrans-Br(CO)4W=CPh and has been shown to undergo the reverse of the decoupling reaction i.e. an H Br-induced coupling of a tert-butylisocyanide with the phenylcarbyne ligand to form 4b. The compositions and structures of the complexes 1 a-5b have been determined by total elemental analyses, IR, 1H NMR, 13C NMR and mass spectra. The spectroscopic results indicate a substantial bond delocalization in the 1-aminoalkyne complexes 4a-4c and a hindered rotation of the diethylamino group in the alkyne ligand of 4c. The barrier to this rotation is calculated to be ca. 14.7 kcal/mol and compared with previously reported diethylaminoalkyne complexes. An X-ray crystallographic study of 5 b has been carried out. The compound crystallizes in the monoclinic space group P 21. The unit cell contains two molecules of 5 b, which have a distorted octahedral coordination geometry with a trans-arrangement of the bromo and the phenylcarbyne ligand. The four isocyanide ligands are slightly bent out of the equatorial plane towards the bromo ligand. Striking features of the structure are the shortest W=Ccarbyne and the longest W —Br bond lengths known for low valent tungsten aryl- and alkylcarbyne complexes indicating a high electron density at tungsten. In addition two isocyanide ligands show a bent geometry at nitrogen, which has been so far reported only for electron-rich isocyanide complexes.

scholarly journals Facile synthesis of novel, known, and low-valent transition metal phosphates via reductive phosphatization

2021 ◽  
Author(s):  
Niklas Stegmann ◽  
Hilke Petersen ◽  
Claudia Weidenthaler ◽  
Wolfgang Schmidt
Keyword(s):  
Transition Metal ◽  
Oxidation States ◽  
Facile Synthesis ◽  
Metal Phosphates ◽  
Low Valent

Novel and known low valent transition metal phosphates (TMPs) are accessible via a novel and facile pathway. The method allows syntheses of TMPs also with reduced oxidation states. The key...

scholarly journals Low-valent dialkoxytitanium(ii): a useful tool for the synthesis of functionalized seven-membered ring compounds

2021 ◽  
Vol 57 (29) ◽  
pp. 3603-3606
Author(s):  
Florent Bodinier ◽  
Youssouf Sanogo ◽  
Janick Ardisson ◽  
Marie-Isabelle Lannou ◽  
Geoffroy Sorin
Keyword(s):  
Grignard Reagent ◽  
Membered Ring ◽  
Ring Compounds ◽  
Low Valent

Herein, we describe unprecedented access to all-carbon or heterocyclic seven-membered ring frameworks from 1,8-ene-ynes promoted by inexpensive low-valent titanium(ii) species, readily available from a combination of Ti(OiPr)4 and Grignard reagent.

scholarly journals Glycan-to-Glycan Binding: Molecular Recognition through Polyvalent Interactions Mediates Specific Cell Adhesion

Molecules ◽  
2021 ◽  
Vol 26 (2) ◽  
pp. 397
Author(s):  
Gradimir Misevic ◽  
Emanuela Garbarino
Keyword(s):  
Cell Adhesion ◽  
Plasma Membranes ◽  
Specific Cell ◽  
Cellular Interactions ◽  
New Paradigm ◽  
Tumor Cell Adhesion ◽  
Self Recognition ◽  
Structural And Functional Properties ◽  
Low Valent

Glycan-to-glycan binding was shown by biochemical and biophysical measurements to mediate xenogeneic self-recognition and adhesion in sponges, stage-specific cell compaction in mice embryos, and in vitro tumor cell adhesion in mammals. This intermolecular recognition process is accepted as the new paradigm accompanying high-affinity and low valent protein-to-protein and protein-to-glycan binding in cellular interactions. Glycan structures in sponges have novel species-specific sequences. Their common features are the large size >100 kD, polyvalency >100 repeats of the specific self-binding oligosaccharide, the presence of fucose, and sulfated and/or pyruvylated hexoses. These structural and functional properties, different from glycosaminoglycans, inspired their classification under the glyconectin name. The molecular mechanism underlying homophilic glyconectin-to-glyconectin binding relies on highly polyvalent, strong, and structure-specific interactions of small oligosaccharide motifs, possessing ultra-weak self-binding strength and affinity. Glyconectin localization at the glycocalyx outermost cell surface layer suggests their role in the initial recognition and adhesion event during the complex and multistep process. In mammals, Lex-to-Lex homophilic binding is structure-specific and has ultra-weak affinity. Cell adhesion is achieved through highly polyvalent interactions, enabled by clustering of small low valent structure in plasma membranes.

{MI(CO)X(CNArDArF2)4} (DArF = 3,5-(CF3)2C6H3; M = Re and Tc; X = Br and Cl) Complexes: Convenient Platforms for the Synthesis of Low-Valent Rhenium and Technetium Compounds

2021 ◽  
Author(s):  
Federico Salsi ◽  
Michael Neville ◽  
Myles Drance ◽  
Adelheid Hagenbach ◽  
Joshua S. Figueroa ◽  
...  
Keyword(s):  
Low Valent

Activation of Nitrogen-Rich Substrates by Low-Valent, Redox-Active Aluminum Species

2021 ◽  
Vol 40 (4) ◽  
pp. 490-499
Author(s):  
Weixing Chen ◽  
Vladimir A. Dodonov ◽  
Vladimir G. Sokolov ◽  
Li Liu ◽  
Evgeny V. Baranov ◽  
...  
Keyword(s):  
Redox Active ◽  
Active Aluminum ◽  
Low Valent
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