Synthesis and characterization of new binuclear boron compounds with bridging guanidinate ligands [Elektronische Ressource] / vorgelegt von Oxana Ciobanu

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INAUGURAL-DISSERTATION zur Erlangung der Doktorwürde der Naturwissenschaftlich-Mathematischen Gesamtfakultät der Ruprecht-Karls-Universität Heidelberg Vorgelegt von Master of Science Oxana Ciobanu aus Cluj-Napoca/Romania Tag der mündlichen Prüfung: 20. November 2009 Synthesis and Characterization of New Binuclear Boron Compounds with Bridging Guanidinate Ligands Gutachter: Prof. Dr. Dr. Hans-Jörg Himmel Prof. Dr. Gerald Linti Dedicated to my parents and loving boyfriend Martin Table of contents Table of contents Zusammenfassung 1 Abstract 2 Abbreviations 3 1. Introduction 6 1.1 Addition/elimination of H to the E-E bond of binuclear main group element 6 2compounds 10 1.2 Diborane(4) compounds 1.3 Some aspects of binuclear coordinative compounds with guanidine 16 ligands 1.4 Aim of the present research 22 1.5 References 23 2. Results and discussion 29 2.1 Synthesis and characterization of new guanidine-borane adducts: 29 H B·hppH and H B·N(H)C(NMe ) 3 3 2 22.1.1 Synthesis 30 2.1.2 Spectroscopic properties 32 2.1.3 Structure determinations 37 2.1.4 Quantum chemical studies of the bonding properties in amine- and guanidine- 43 borane adducts 2.

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INAUGURAL-DISSERTATION




zur

Erlangung der Doktorwürde

der Naturwissenschaftlich-Mathematischen

Gesamtfakultät

der Ruprecht-Karls-Universität

Heidelberg










Vorgelegt von

Master of Science Oxana Ciobanu

aus Cluj-Napoca/Romania









Tag der mündlichen Prüfung: 20. November 2009







Synthesis and Characterization of New
Binuclear Boron Compounds with
Bridging Guanidinate Ligands


























Gutachter: Prof. Dr. Dr. Hans-Jörg Himmel
Prof. Dr. Gerald Linti










Dedicated to my parents and loving boyfriend Martin
























Table of contents


Table of contents

Zusammenfassung 1
Abstract 2
Abbreviations 3
1. Introduction 6
1.1 Addition/elimination of H to the E-E bond of binuclear main group element 6 2
compounds
10 1.2 Diborane(4) compounds
1.3 Some aspects of binuclear coordinative compounds with guanidine 16
ligands
1.4 Aim of the present research 22
1.5 References 23
2. Results and discussion 29
2.1 Synthesis and characterization of new guanidine-borane adducts: 29
H B·hppH and H B·N(H)C(NMe ) 3 3 2 2
2.1.1 Synthesis 30
2.1.2 Spectroscopic properties 32
2.1.3 Structure determinations 37
2.1.4 Quantum chemical studies of the bonding properties in amine- and guanidine- 43
borane adducts
2.2 Experimental and computational studies of the thermal and catalytic 48
dehydrogenation of H B·hppH and H B·N(H)C(NMe ) 3 3 2 2
2.2.1 Quantum chemical studies 48
2.2.1.1 Thermal dehydrogenation 49
2.2.1.2 Catalytic dehydrogenation 54
2.2.2 Experimental studies 58
2.2.2.1 Thermal and catalytic dehydrogenation of HB·hppH 58 3
2.2.2.2 Thermal and cataly B·N(H)C(NMe ) 63 3 2 2
2.3 Synthesis and characterization of new binuclear boron hydrides containing 71
two bridging guanidinate (hpp) ligands
72 2.3.1 Synthesis and characterization of [H B( -hpp)] 2 2
75 2.3.2 Synthesis and characterization of [HB( -hpp)] 2
- - 79 2.3.3 Synthesis and characterization of [H B ( -hpp) ]X (X = I or Cl ) 3 2 2Table of contents


79 2.3.3.1 Synthesis and characterization of [H B ( -hpp) ]I 3 2 2
85 2.3.3.2 Synthesis and characterization of [H B ( -hpp) ]Cl 3 2 2
2.3.3.3 Quantum chemical studies 88
2.4 Synthesis and characterization of new binuclear boron monocation 92
containing three bridging guanidinate (hpp) ligands
92 2.4.1 Synthesis and characterization of [Cl B ( -hpp) ]BCl 2 2 3 4
2.5 Synthesis and characterization of new binuclear boron di- and 95
monocations containing two bridging guanidinate (hpp) ligands
95 2.5.1 Synthesis and characterization of [{(Me (H)N)B( -hpp)} ]Cl 2 2 2
1012.5.2 Synthesis and characterization of [(Me N)B ( -hpp) (NHMe )]Cl and [ClB ( -2 2 2 2 2
hpp) (NHMe )]Cl 2 2
- 1092.5.3 Synthesis and characterization of [{(Me (H)N)B( -hpp)} ]X , (X = OTf and 2 2 2
-[B(C F ) ] ) 6 5 4
- - - 1142.5.4 Thermal reactions of [{Me (H)N)B( -hpp)} ]X , (X = Cl , OTf and [B(C F ) ] ) 2 2 2 6 5 4
2.6 References 118
3. Conclusions 124
4. Experimental part 131
4.1 General Comments 131
1334.2 Synthesis of new guanidine – borane adducts
4.2.1 Synthesis of HB·hppH 1333
4.2.2 Synthesis of H B·N(H)C(NMe ) 1353 2 2
4.3 Thermal and catalytic dehydrogenation of guanidine-borane adducts 136
4.3.1 Thermal dehydrogenation of H B·hppH at 80°C 1363
4.3.2 Thermal dehydrogenation of H B·hppH at 110°C 1363
4.3.3 Thermal dehydrogenation of the H B·N(H)C(NMe ) at 80°C and 110°C 1373 2 2
4.3.4 Catalysed dehydrogenation of H B·hppH at 80°C in the presence of 1373
[Rh(1,5-COD)Cl] 2
4.3.5 Catalysed dehydrogenation of the H B·N(H)C(NMe ) at 80°C in the presence 1373 2 2
of [Rh(1,5-COD)Cl] 2
1374.3.6 Dehydrogenation of H B·hppH at 115°C in the presence of [(PPh ) RhCl] 3 3 3Table of contents


4.3.7 Dehydrogenation of the H B·N(H)C(NMe ) at 80°C in the presence of 1383 2 2
Cp TiCl /nBuLi 2 2
4.4 Synthesis of new binuclear boron hydrides containing two bridging 138
guanidinate (hpp) ligands
4.4.1 Synthesis of [H B( μ-hpp)] 1382 2
4.4.2 Synthesis of [HB( μ-hpp)] 1402
1424.4.3 Synthesis of [H B ( -hpp) ]I 3 2 2
1444.4.4 Synthesis of [H B ( -hpp) ]Cl 3 2 2
4.5 Synthesis and characterization of new binuclear boron monocation 145
containing three bridging guanidinate (hpp) ligands
1454.5.1 Synthesis of [B Cl ( -hpp) ]BCl 2 2 3 4
4.6 Synthesis and characterization of new binuclear boron di- and 146
monocations containing two bridging guanidinate (hpp) ligands
4.6.1 Synthesis of starting materials 146
4.6.1.1 Synthesis of Tris(pentafluorophenyl)borane 146
4.6.1.2 Synthesis of Lithium tetrakis(pentafluorophenyl)borate 148
4.6.1.3 Synthesis of 1,2-Dichloro-1,2-(bisdimethyldiamino)-diborane 149
4.6.2 Synthesis of [{(Me (H)N)B( μ-hpp)} ]Cl 1502 2 2
4.6.3 Synthesis of [(Me N)B( -hpp)] and [(Me N)B ( μ-hpp) (NHMe )]Cl 1522 2 2 2 2 2
4.6.4 Synthesis of [ClB ( μ-hpp) (NHMe )]Cl 1532 2 2
4.6.5 Synthesis of [{Me (H)NB( μ-hpp)} ][OTf] 1542 2 2
4.6.6 Synthesis of [{Me (H)NB( μ-hpp)} ][B(C F ) ] 1562 2 6 5 4 2
4.7 References 158
5. Supplementary material 159
5.1 Crystal data and refinement details 159
5.2 Quantum chemical calculations 184

6. Publications 188

7. Acknowledgments 190

Zusammenfassung



Zusammenfassung

Diese Arbeit beschäftigt sich mit der Synthese, chemischen Reaktionsfähigkeit und
Charakterisierung neuer zweikerniger Borverbindungen, welche verbrückte
Guanidinat Liganden enthalten.
Die Basenaustausch-Reaktion zwischen H B·NMe und den Guanidinen hppH oder 3 3
N(H)C(NMe ) resultierte in neuen Guanidin-Boran-Addukten HB·hppH und 2 2 3
H B·N(H)C(NH ) , welche als Ausgangsubstanzen zur thermischen und katalytischen 3 2 2
Dehydrierung verwendet wurden. Der Reaktionsmechanismus wurde mit Hilfe
quantenchemischer (DFT) Rechnungen mit der Verwendung des H B·N(H)C(NMe ) 3 2 2
Modells aufgeklärt. Im Gegensatz zu H B·hppH führt die thermische Dehydrierung 3
von H B·N(H)C(NMe ) zu einer Zersetzung der Ausgangsverbindung und Bildung 3 2 2
von polymeren Methyliminoboran [HBNMe]. Zum näheren Verständnis des n
Zersetzungsvorgangs wurden quantenchemische (DFT) Rechnungen hinzugezogen.
Eine schnellere Dehydrierung konnte durch einen Katalysator erreicht werden.
Katalytische Dehydrierung von H B·hppH führte zu einem zweikernigen Borhydrid 3
[H B( -hpp)] , welches zwei Guanidinat (hpp) Liganden enthielt. Weitere (reduktive) 2 2
katalytische Dehydrierung von [H B( -hpp)] ergibt ein neues doppelt 2 2
basenstabilisiertes Diboran(4) [HB( -hpp)] . Das Diboran(4) [HB( -hpp)] reagiert 2 2
- - +über eine oxidative Addition mit HX (X = Cl oder I ) zu stabilen B H - analogen 2 5
Verbindungen [H B ( -hpp)]X. Zur Aufklärung der Bindungseigenschaften im 3 2 2
+zweikernigen B(III) Hydrid [H B ( -hpp) ] -Kation wurden quantenchemische (DFT) 3 2 2
Rechnungen hinzugezogen. Die Reaktion zwischen BCl und hppH führte auf 3
direktem Weg zu der Verbindung [Cl B ( -hpp) ]BCl , die drei Guanidinat (hpp) 2 2 3 4
Liganden enthält. Dies legt einen weitaus komplizierteren Reaktionsmechanismus
als bei der Umsetzung von H B·NMe mit hppH nahe. B Cl (NMe ) reagiert mit 3 3 2 2 2 2
hppH zu [{(Me (H)N)B( -hpp)} ]Cl , dem ersten Vertreter eines binuklearen B(II)-2 2 2
Kations mit einer direkten B-B-Bindung. Die Reaktion zwischen [{(Me (H)N)B( -2
hpp)} ]Cl und AgOTf oder Li[B(C F ) ] führte zu Verbindungen mit schwach 2 2 6 5 4
koordinierenden Anionen. Die thermische Zersetzung der entstehenden
- - -Verbindungen [{(Me (H)N)B( -hpp)} ]X (X = Cl , OTf und [B(C F ) ] ) wurde mit Hilfe 2 2 2 6 5 4
von NMR-Daten untersucht.
1Abstract



Abstract

This work is concerned with the synthesis, chemical reactivity, and characterization
of new binuclear boron compounds containing bridging guanidinate ligands.
The guanidine-borane adducts H B·hppH and H B·N(H)C(NMe ) , accessed by a 3 3 2 2
base exchange reaction between H B·NMe and the guanidine derivative hppH or 3 3
N(H)C(NMe ), were targeted as precursors in thermal and catalytic 2 2
dehydrogenations. The reaction mechanism for these experiments was elucidated by
means of quantum chemical (DFT) calculations on the model H B·N(H)C(NH ) . In 3 2 2
contrast to HB·hppH, the thermal dehydrogenation of H B·N(H)C(NMe ) is 3 3 2 2
accompanied by decomposition, leading to methylimino borane oligomers,
[HBNMe] . The decomposition pathway was studied and understood with the aid of n
quantum chemical calculations. Faster dehydrogenation could be initiated by addition
of a catalyst. The dehydrogenation of H B·hppH in presence of a catalyst leads to the 3
binuclear B(III) hydride [H B( -hpp)] , containing two guanidinate (hpp) ligands. 2 2
Further (reductive) catalytic dehydrogenation of [H B( -hpp)] gave the double-base 2 2
stabilized diborane(4) [HB( -hpp)] , featuring direct B-B bonding. Besides, [HB( -2
- -hpp)] undergoes an oxidative addition reaction with HX (X = Cl or I ), respectively 2
+which afforded [H B ( -hpp) ]X, representing a stable B H analogues. Quantum 3 2 2 2 5
chemical (DFT) calculations were carried out to analyse the bond properties in the
+cationic binuclear B(III) hydride [H B ( -hpp) ] . The reaction between BCl and 3 2 2 3
hppH lead to [Cl B ( -hpp) ]BCl containing three guanidinate (hpp) ligands, which 2 2 3 4
suggests that this reaction has a much more difficult mechanism than the
H B·NMe /hppH reaction. B Cl (NMe ) reacts with hppH to yield [{(Me (H)N)B( -3 3 2 2 2 2 2
hpp)} ]Cl , featuring the first representative of two B(II) cations with direct B-B 2 2
bonding. Further reactions between [{(Me (H)N)B( -hpp)} ]Cl and AgOTf or 2 2 2
Li[B(C F ) ] yielded new salts with weakly coordinating anions. Additionally, thermal 6 5 4
- - -decomposition of [{(Me (H)N)B( -hpp)} ]X (X = Cl, OTf and [B(C F ) ]) was 2 2 2 6 5 4
investigated on the basis of NMR experiments.
2 Abbreviations
Abbreviations

Ac Acetyl
Bn Benzyl
Bu Butyl group
tBu tert-Butyl group
n nBuLi Butyllithium
B3LYP Becke, three-parameter, Lee-Yang-Parr
BSSE Basis Set Superposition Error
ca. circa
cat cathecolato
COD 1,5-Cycloctadiene
Cp Cyclopentadienyl
CPCM the Conductor-like Polarizable Continuum Model
Cy Cyclohexyl
d doublet
DFT Density Functional Theory
DMSO Dimethyl sulfoxide
E Energy
EA Elemental Analysis
EI Electron Ionization
ESI Electrospray ionization
Et Ethyl group
g gram
G Gibbs free energy
GIAO Gauge-Including Atomic Orbital
H Enthalpy
h hour
hppH 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine
HR High Resolution
HRMAS High Resolution Magic Angle Spinning
Htbn 2,3,5,6,7,8-hexahydroimidazo[1,2-a]pyrimidine
Htbo 2,3,5,6-tetrahydro-1H-imidazo[1,2-a]imidazole
3 Abbreviations
Hz Hertz
ip in phase
IR Infrared
J Coupling constant
K Kelvin
kHz kilohertz
kJ kilojoule
LANL2DZ Los Alamos National Laboratory 2-double-z
m multiplet (NMR spectroscopy), medium (IR spectroscopy)
M Mechanism
Me Methyl
MHz Megahertz
ml millilitre
mmol millimol
MP Møller-Plesset Perturbation theory
MS Mass Spectrum, Mass Spectrometry
m/z mass-to-charge ratio
nm nanometre
NMR Nuclear Magnetic Resonance
oop out of phase
OTf Trifluoromethanesulfonate, CF SO - 3 3
Ph Phenyl
pin pinacolato
pm picometre
ppm parts per million
pz pyrazol
q quartet
qui quintet
R Alkyl or Aryl
[Rh] [Rh(1,5-COD)Cl] 2
RHF Restricted Hartree-Fock
RT Room temperature
s singlet (NMR spectroscopy), strong (IR spectroscopy)
4