Elektronische Struktur von E 2 H 4 D 2 h: σ π H π ^= H E π σ π σ σ in C 2 H 4 8 in b MO, 4 in ab MO in B 2 H 4 12e N = 2 10e N = 1 höhere Bindungsordnung durch Reduktion Folie 1
Elektronische Struktur von E 2 H 2 D h σ π in C 2 H 2 10e N = 3 in B 2 H 2 8e N = 2 und Triplettgrundzustand hochreaktiv, instabil π σ σ B 2 H 6 hν 4 K H B B H 1 1 durch Photoionisation aus B 2 H 6 in Edelgasmatices bei 4K Charakterisierung über ESR Triplett σ Folie 2
Neutral Platinum Borylenecomplexes Br PCy 3 Pt B N SiMe 3 + Cl 3 Br PCy 3 Pt B N Cl 3 SiMe 3 PCy 3 PCy 3 Pt-B = 196.0(3) pm Pt-Br = 255.16(4) pm B-N = 126.0(4) pm Pt-B = 190.4(3) pm Pt-Br = 252.80(2) pm B-N = 133.0(3) pm J. Am. Chem. Soc. 2007, 129, 10350.
Potentialenergiefläche H 2 C=CH 2 vs. H 2 Si=SiH 2 cf. the more diffuse 3s and 3p orbitals (radial distribution functions) H 2 Si=SiH 2-250kJ/mol bei 215 pm http://www.chm.davidson.edu/ronutt/che115/radial/radial..htm H 2 C=CH 2-739 kj/mol bei 132.3 pm Includes preparation energy to produce triplet, i.e. singlet-triplet gap Ziegler et al., J. Am. Chem Soc. 1994, 116, 3667. http://pubs.acs.org/doi/pdf/10.1021/ja00088a001
7 Farbigkeit von Disilenen West 1981 Sakurai 1994 R=SiMe t Bu 2 R Si R Si R R Sekiguchi 2004 400 500 λ [nm] 600 700 R R R R Si Si Mes= Me Me R Si Si R Me MeMe Me Me Kira et al., Angew. Chem. Int. Ed. 2004, 45, 6371. http://dx.doi.org/110.1002/anie.200602214
Boranes - Synthesis On a Hydride of Boron F. Jones, J. Chem. Soc. 1879, 35, 41. Mg (magnesium) "B 2 O 3 " "Mg 3 B 2 " HCl "BH 3 " At the turn of the 19th century, hydrides were known for all non-metals, except boron. Pioneering work by fred Stock (1876-1946) since 1909 Mg (magnesium) "B 2 O 3 " "Mg 3 B 2 " HCl complex mixture of boranes and silanes distillation B 4 H 10,,Borwasserstoffe A. Stock, C. Massenez, Ber. Dtsch. Chem. Ges. 1912, 45, 3539.
Diborane(6) - Structure and Bonding B B B B H H H H H H? C C? H H H H H H H H H H H H Ethane C 2 H 6 : 14 electrons in 7 pairs (bonds) every carbon atom employs 8 electrons classical (electron precise) bonding situation Diborane(6) B 2 H 6 : 12 electrons non-classical (electron deficient) bonding situation Selected examples attempting to describe the correct constitution and bonding of diborane(6)
Diborane(6) - Structure and Bonding Diborane(6) B 2 H 6 : structure confirmed by X-ray and electron diffraction 4 terminal and 2 bridging hydrogens not consistent with a classical bonding description William Lipscomb born 1919 Nobel Prize in Chemistry 1976 W. N. Lipscomb: "Boron Hydrides", W. A. Benjamin Inc., New York 1963. anti-bonding MO non-bondig MO Rationale: 2c-2e bonds for terminal hydrogens 3c-2e bonds for bridging hydrogens electronic structure can not be described by Lewisformalism or Valence Bond theory breakthrough for Molecular Orbital theory bonding MO
Higher Boranes - Structure and Bonding Classification of higher boranes: Kenneth Wade, FRS born 1932 counting scheme (based on MO theory) to predict the cluster geometry from the formula Wade s Rules rationale for the structural/electronic relationships between closo- nido- and arachno-boranes applicable to heteroboranes, metallaboranes, boron-free polynuclear species (e.g. Zintl-anions) extended to metal clusters Wade- Mingos-Rules K. Wade, J. Chem. Soc. Chem. Commun.1971, 792. Examples: B 12 H 12 : 13 electron pairs, 12 vertices (n+1) closo B 11 H 15 : 13 electron pairs, 11 vertices (n+2) nido B 10 H 16 : 13 electron pairs, 10 vertices (n+3) arachno
Cluster-bindende Orbitale von [B 6 H 6 ] 2- E MO n + 1 bindende Molekülorbitale t 2g 6 x H B t 1u a 1g
Für den Clusteraufbau zur Verfügung stehende MO s eines B-H Gerüstbausteines E MO tangentiale Orbitale 2 x "p" radiales Orbital 1 x "sp" H B ("sp"-hybridisiert)
Beispiele: B 5 H 9 nido-pentaboran(9) B 4 H 10 arachno-tetraboran(10)
B 6 H 10 nido-hexaboran(10) B 5 H 11 arachno-pentaboran(11)
[B 12 H 12 ] 2 closo -Dodekahydrododekaborat(2-) B 12 H 10 (CO) 2 closo -1,12-Dicarbonyldodekaboran(10) CO CO
Beispiele: B 8 Cl 8 Borsubhalogenide B n X n (X = Hal, n = 6, 8-12) hypercloso - Octachlorooctaboran(8) B 9 Cl 9 hypercloso - Nonachlorononaboran(9) Derartige hypercloso-cluster besitzen closo-strukturen.
Zintl-Ionen: [Sn 8 ] 6- Clustertyp? arachno 6- [Sn 9 ] 4- Clustertyp? nido 4-
[Ge 9 ] 2- Clustertyp? closo 2- [Pb 5 ] 2- Clustertyp? closo 2-
[Si 4 ] 6- (in Ba 3 Si 4 ) Clustertyp? arachno
6 69 R 18 3- und 77 R 20 2- aus X und LiN(SiMe 3 ) 2 (60 C) aus uminium(i)chlorid outer shell 18 69 R 18 3- aus uminium(i)iodid 12 1 38 20 Ox = (18 3)/69 = 0.217 12 1 44 77 R 20 2- Ox = (20 2)/77 = 0.234
7 14 R 6 I 6 2- aus I und LiN(Me 3 Si) 2 (25 C) Paddle wheel structure Ox = (12 2)/14 = 0.714 = bare aluminium = iodide-bearing = amide-bearing Schnöckel et al., Angew. Chem. Int. Ed. 2000, 39, 799. http://www3.interscience.wiley.com/cgi-bin/fulltext/70001477/pdfstart
8 12 R 8 aus Cl und LiN(Me 3 Si) 2 (25 C) rhomboids uminium Bulk ccp octahedra Ox = (8 1)/12 = 0.583 Schnöckel et al., Chem. Commun. 1999,1933. http://dx.doi.org/10.1039/a904247d
Voraussetzung für hohen Umsatz ist die exakte Stöchiometrie (1:1) der Reaktanden, d.h. Edukte müssen möglichst rein vorliegen. Polykondensationen beruhen auf der Reaktion bifunktioneller Moleküle; funktionalisierte anorganische/metallorganische Spezies sind i.a. wesentlich reaktiver als organische und kaum in ausreichender Reinheit für hohe Umsätze bei Polykondensationen darstellbar.
z x z y N P N P hybridisation at N (sp 2 ) and P (sp 3 ) showing a lp on N y x P P Erklärung der Bindungsverhältnisse unter Beteiligung von d- Orbitalen am Phosphor (sog. π -Bindung wg. Knotenebene am P und Unterbrechung der Delokalisation) trifft nicht zu. N N N N π interactions in the ring plane between lp on N and d-ao s on adjacent P z y x P P N N N N π interactions between p z AO on N and d-ao s on adjacent P