π-Bonding and the Lone Pair Effect in Multiple Bonds between Heavier Main Group Elements

This review is essentially an update of one entitled “πBonding and The Lone Pair Effect in Multiple Bonds Between Heavier Main Group Elements” which was published more than 10 years ago in this journal.1 The coverage of that survey was focused on the synthesis, structure, and bonding of stable compounds2 of heavier main group elements that correspond to the skeletal drawings reproduced in Tables 1 and 2. A row of numbers is listed at the bottom of each column in these tables. This refers to the number of stable complexes from each class that are currently known. The numbers in parentheses refer to the number of stable species that were known at the time of the previous review. Clearly, many of the compound classes listed have undergone considerable expansion although some remain stubbornly rare. The most significant developments for each class will be discussed in detail under the respective sections. As will be seen, there are also a limited number of multiple bonded heavier main group species that do not fit neatly in the classifications in Tables 1 and 2. However, to keep the review to a manageable length, the limits and exclusions, which parallel those used earlier, are summarized as follows: (i) discussion is mainly confined to compounds where experimental data on stable, isolated species have been obtained, (ii) stable compounds having multiple bonding between heavier main group elements and transition metals are not generally discussed, (iii) compounds in which a multiple bonded heavier main group element is incorporated within a ring are generally not covered, and (iv) hypervalent main group compounds that may incorporate faux multiple bonding are generally excluded. Such compounds are distinguished from those in Tables 1 and 2 in that they apparently require the use of more than four valence bonding orbitals at one or more of the bonded atoms. The remainder of this review is organized in a similar manner to that of the previous one wherein the compounds to be discussed are classified according to those summarized in Tables 1 and 2. The key unifying feature of almost all molecules discussed in this review is that they are generally stabilized by the use of bulky substituents which block associative or various decomposition pathways.3 Since the previous review was published in 1999, several review articles that cover parts of the subject matter have appeared.4

π-Bonding and the Lone Pair Effect in Multiple Bonds Involving Heavier Main Group Elements: Developments in the New Millennium

In this review the processes occurring on the treatment of triphenylphosphane with tetrachloromethane are first reported; a key role is played here by (trichloromethyl)phosphonium chloride which reacts with a further amount of the phosphane to give the stable salt [chloro(triphenylphos-phoranediyl)methyl]triphenylphosphonium chloride by way of dichlorophosphorane and (dichloromethylene)phosphorane that is detectable only as an intermediate. The preparative application of the two-component system as a chlorinating, dehydrating, and P—N-linking reagent is ascribable to “phosphorylation” of the substrate in question through several reactive species. In these applications the reactions with the substrate compete with reactions of the two-component system with itself, so that the overall course of the reaction is in nearly all cases much more complex than was previously assumed. Nevertheless. very good results can be achieved by the use of this reagent, high yields and mild reaction conditions being characteristic.

Tertiary Phosphane/Tetrachloromethane, a Versatile Reagent for Chlorination, Dehydration, and P ? N Linkage

Recent advances in the staudinger reaction

The chemistry of recently isolated naturally occurring quinazolinone alkaloids

Dischwefeldichlorid reagiert mit Acetonitril uber die Stufen Chlor- und Dichloracetonitril zu 4,5-Dichlor-1,2,3-dithiazolium-chlorid (1). Das Reaktionsverhalten von 1 gegenuber protonen-aktiven Stoffen wird durch die nucleophile Substitution des Chlors am Kohlenstoff C-5 gepragt. Substrate, die wie H2O, H2S, primare Amine und Sulfonamide uber zwei aktive Wasserstoff-atome verfugen, reagieren zu den kovalenten 4-Chlor-5H-1,2,3-dithiazol-Derivaten 2,3,5. Phenole werden von 1 in o- oder p-Stellung elektrophil zu den 4-Chlor-5-(hydroxyphenyl)-1,2,3-dithiazolium-chloriden 9a–d substituiert. Durch HCl-Eliminierung erhalt man aus diesen tiefviolette metallisch glanzende Kristalle der betainartigen Neutralmolekule 10a,b. Nach Rontgen-strukturanalyse von 10a liegen die planaren Molekule in stapelformiger helicaler Anordnung vor. – Mit Chlor entstehen aus 1 unter Ringoffnung die Verbindungen 14, 15, entsprechend wird aus 2 mit Chlor 2-Chlor-2-(chlorthioimino)acetylchlorid (18) erhalten.



Synthesis and Reactions of 4,5-Dichloro-1,2,3-dithiazolium Chloride



Disulfur dichloride reacts with acetonitrile via chloro- and dichloroacetonitrile to give finally 4,5-dichloro-1,2,3-dithiazolium chloride (1). The reactivity of 1 with proton-active compounds is determined by the nucleophilic substitution of the chlorine at carbon atom C-5. Substrates like H2O, H2S, primary amines, and sulfonamides, having two active hydrogen atoms, form the covalent 4-Chloro-5H-1,2,3-dithiazole derivatives 2, 3, 5. 1 reacts with phenols in o- or p-position by an electrophilic attack to form 4-chloro-5-(hydroxyphenyl)-1,2,3-dithiazolium chlorides 9a–d. HCl elimination from these leads to deep violet, metallic-reflecting crystals of the betaine-like neutral molecules 10a, b. X-ray analysis shows a planar structure of 10a and a molecular arrangement of a right and a left helix. Ring cleavage of 1 with chlorine gives compounds 14, 15; correspondingly, 2 reacts with chlorine to yield 2-chloro-2-(chlorothioimino)acetyl chloride (18).

Synthese und Reaktionen des 4,5‐Dichlor‐1,2,3‐dithiazolium‐chlorids

Die Umsetzung des silylierten Phosphaalkens 1 mit Hexachlorethan (2) ergibt das Chlorphosphaalken 3, welches mit weiterem 1 unter Chlortrimethylsilan-Abspaltung zum ersten 2,3-Diphosphabutadien 6 reagiert. Dieses last sich ebenfalls aus dem persilylierten Diphosphan 4 und 2,2-Dimethylpropionylchlorid (5) darstellen. Die spektroskopischen und Rontgenstrukturdaten von 6 werden diskutiert. Versuche zur Darstellung der 1,4-Diphosphabutadiene 11a, b aus den Organylbis(trimethylsilyl)phosphanen 9a, b und Oxalylchlorid (10) ergeben die entsprechend substituierten 3,4-Diphosphacyclobutene 12a, b. Die Reaktion von 1 mit Phosgen (14a) und dem Isocyaniddichlorid 14b liefert anstelle der erwarteten 1,3-Diphosphabutadiene 16a, b die 1,3-Diphosphacyclobutene 17a, b, deren Struktur durch die Rontgenbeugungsanalyse von 17a gesichert ist. Die Bildung der Cyclobutene 12a, b und 17a, b wird diskutiert.



Low Coordinated Phosphorus Compounds, Diphosphabutadienes



The reaction of the silylated phosphaalkene 1 with hexachloroethane (2) yields the chlorophosphaalkene 3, which reacts with additional 1 under chlorotrimethylsilane elimination to give the first 2,3-diphosphabutadiene 6. This can be prepared as well from the persilylated diphosphane 4 and 2,2-dimethylpropionyl chloride (5). The spectroscopic and x-ray data of 6 are discussed. Experiments for the preparation of the 1,4-diphosphabutadienes 11a, b from the organylbis(trimethylsilyl)phosphanes 9a, b and oxalyl chloride yield the correspondingly substituted 3,4-diphosphacyclobutenes 12a, b. The reaction of 1 with phosgene and isocyanide dichloride 14b yields instead of the expected 1,3-diphosphabutadienes 16a, b the 1,3-diphosphacyclobutenes 17a, b, whose structure is affirmed by x-ray structure determination of 17a. The formation of the cyclobutenes 12a, b and 17a, b is discussed.

Niederkoordinierte Phosphor-Verbindungen, 17. Diphosphabutadiene

Die Synthese neuartiger, silylierter Bisiminophosphorane des Typs Ph2P(NSi(CH3)3)(CH2)(n)PPh2(NSi(CH3)3) 2a, b und c mit n = 1, 2, 3 und des analog gebauten cyclischen Silins 5 erfolgt durch Umsetzung der betreffenden Alkylenbisphosphine mit Silylaziden. Die offenkettigen Vertreter 2a und b werden von atherischer HCl desilyliert; sie kondensieren – ebenso wie 5 – mit den Fluorphosphoranen PhxPF5–x(x = 0, 1) unter Fluorsilanabspaltung zu den ionischen, partiell fluorierten Diphosphazaphosphonium-Ringsystemen 7a, b und 8. Die Identifizierung und Charakterisierung der Reaktionsprodukte erfolgt vor allem durch 19F- und 31P-NMR-Spektroskopie.



The Preparation of Silylated Alkylene-Bisiminophosphoranes and the Cyclisation with Phosphorus(V) Fluorides thereof



New silylated bisiminophosphoranes of the type Ph2P(NSi(CH3)3)(CH2)n Ph2P(NSi(CH3)3) 2a, b and c (n = 1, 2, 3) and the similary structured cyclic siline 5 are prepared by reaction of the corresponding alkylene-bisphosphines with silylazides.



Using etheric HCl, the opened chain compounds 2a and b, are desilylated; they undergo condensation reactions with fluorophosphoranes PhxPF5–x(x = 0, 1) – the same as 5 – splitting off fluorosilane forming the partially fluorinated ionic diphosphaza-phosphonium ring systems 7a, b and 8.

Darstellung silylierter Alkylen‐bisiminophosphorane und ihre Cyclisierung mit Phosphor(V)‐fluoriden

Über die gemeinsame Einwirkung von Phosphinen und Tetrachlorkohlenstoff auf Ammoniak (Derivate), IV. Notiz über eine neue Carbodiimid-Synthese

Bis(diorganylphosphino)methane 3 konnen leicht durch Halosilanabspaltung aus Diorganyl-[(trimethylsilyl)methyl]phosphanen 1 und Chlororganylphosphanen 2 gewonnen werden. Neben ungleich substituierten Di(phosphino)methan-Derivaten (3b, c) und dem ersten methylenverbruckten Triphosphan 4 wurde auch ein gemischt arsino-phosphino-substituiertes Methan (3d) hergestellt. Die Einwirkung von Alkalimetallen auf Bis(diphenylphosphino)methan (3a) fuhrt wider Erwarten nicht zur Abspaltung eines Phenylrestes sondern zur Spaltung der PCP-Atomsequenz.

Rolf Appel

Papers

Synthese und Reaktionen des 4,5‐Dichlor‐1,2,3‐dithiazolium‐chlorids

Niederkoordinierte Phosphor-Verbindungen, 17. Diphosphabutadiene

Darstellung silylierter Alkylen‐bisiminophosphorane und ihre Cyclisierung mit Phosphor(V)‐fluoriden

Über die gemeinsame Einwirkung von Phosphinen und Tetrachlorkohlenstoff auf Ammoniak (Derivate), IV. Notiz über eine neue Carbodiimid-Synthese

Über ein neues Darstellungsverfahren und eine ungewöhnliche Spaltung der Methylenbis(diorganylphosphane) durch Alkalimetalle