Oklahoma State University

Synthesis and Characterization of Germanium Catenates

Our research focuses on the synthesis, characterization, and properties of inorganic and organometallic compounds of germanium and other main group elements.  The two main areas of research currently underway in the group are preparation of catenated germanium compounds and the synthesis and properties of inorganic complexes obtained from the reactions of bulky metal(II) amides with polyfunctional phenolic substrates.

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Although compounds containing catenated germanium atoms structurally resemble saturated hydrocarbons their physical properties more closely mirror those of conjugated unsaturated hydrocarbons resulting from their inherent σ-delocalization. The optical and electronic properties of oligogermanes vary with the length of the germanium-germanium backbone and the identity of the attached organic substituents.  Specifically, the absorption maximum of these species undergoes a red shift as the length of the Ge-Ge backbone is increased and also as the bulk of the attached organic side groups increases.  Furthermore, the oxidation potential of the oligomers decreases with increasing chain length and their ability to transfer electron density to organic acceptor molecules increases with this physical characteristic.  Therefore, these physical properties can be tuned by variation of the composition of the individual molecules.

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Equation 1.

 

 

Previous routes for the synthesis of small-molecule catenated germanium compounds have been met with a number of complications, including low yields and the formation of mixtures of products.  We have employed the hydrogermolysis reaction between a germanium amide and a germanium hydride for the synthesis of discrete oligomers instead of product mixtures.  The reaction proceeds via the formation of an a-germyl nitrile that is the active species in the Ge - Ge bond forming reaction (equation 1).  The a-germyl nitrile is formed by reaction of the germanium amide with acetonitrile as the solvent. This method can be used for the synthesis of small molecules containing two or three Ge atoms, or for the stepwise construction of linear oligomeric chains (Scheme 1) via combination with a hydride protection/deprotection strategy.  This allows addition of the individual germanium atoms one at a time, permitting for the first time a systematic variation of the organic substituents attached to the Ge - Ge backbone.

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Scheme 1

We also recently prepared two rare examples of branched germanium oligomers (Scheme 2) and the structure of (Ph3Ge)3GePh was obtained (Figure 2), which represents the first structurally characterized branched germanium oligomer.  The system containing ethoxyethyl side groups should be useful for the construction of two-dimensional arrays of Ge atoms which should exhibit additional intriguing physical properties.  We have used UV/visible spectroscopy to probe the absorption characteristics of these molecules either alone or in solutions with tetracyanoethylene (TCNE) which generates charge transfer (CT) complexes and provides information concerning their electron donor abilities.  We have obtained electrochemical data for these molecules using cyclic voltammetry which shows that the oxidation potential of these species depends on both the number of attached Ge atoms and the identity of the organic substituents.

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Scheme 2branched2.gif Figure 2

Reactions of Bulky Metal(II) Amides with Polyfunctional Phenols

A second major research project being carried out in our group involves the reactions of bulky metal(II) amides M[N(SiMe3)2]2·n THF (M = Be, Zn, Cd, Hg, Ge, Sn, Pb; n = 0.M = Mg, Ca, Sr; n = 2) with polyfunctional phenols including binaphthols and calix[n]arenes.The outcome of the reactions of these amides with 3,3'-disubstituted binaphthols is highly dependent on the identity of the metal.When M = Be, Zn, or Ge, one -OH group of the binaphthol is converted to a -OSiMe3 moiety, leaving the second hydroxyl available for further reactivity.However, when the metal is larger (M = Mg, Ca, Sr, or Sn) the generation of a polymeric material is observed.Finally, the heavier group 12 amides (M = Cd or Hg) result in the conversion of these species to 1,7-disubstituted peri-xanthenoxanthanes by a facile process.These products are potentially useful as organic light emitting species or conductive materials.

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Mercury Reactions

 

 

 

 

 

 

Treatment of calix[n]arenes (n = 4, 6, or 8) with Ge[N(SiMe3)2]2 furnishes compounds having Ge2O2 (n = 4 or 8) or Ge2NO (n = 6) rhombi present in their solid state structures.The crystal structures of three germanium calixarenes are shown below.The formulation of the calix[6]arene complex was unexpected and the structure contains unusual -OSi(H)(NH2)2 groups as well as an uncommon -NH2- group bridging two germanium centers.The calix[4]- and calix[8]arene complexes are of interest since they contain germanium in the +2 oxidation state, where the Ge centers have a lone pair of electrons available for binding to coordiatively unsaturated transition metal complexes.Thus, these species might serve as platforms for the support of multiple luminescent, electrochemically active, or magnetic complexes.Treatment of the calix[8]arene species with Fe2(CO)9 generated the octa-iron species by a redox process which converted the germanium centers to the +4 oxidation state with concomitant reductive

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decarbonylation of the Fe2(CO)9 species.

 

Structure of {Calix[8]arene}Ge4.  The Ge atoms are shown in orange and the oxygen aroms in red.

 

 

 

 

 

 


List of Publications

Publications from Graduate Research (University of Chicago, Northwestern University):
 
1.Charles S. Weinert, Ilia A. Guzei, Arnold L. Rheingold, and Lawrence R. Sita* “Heterocumulene Metathesis of Pb[N(SiMe3)2]2.  High-Yield Syntheses of the Heteroleptic Dimer {Pb[N(SiMe3)2](m-OSiMe3)}2 and the Novel Lead(II) Oxo Cluster Pb7(m3-O)( m4-O)( m-OSiMe3)10.” Organometallics 1998, 17, 498-500.
 
2.Kazusato Shibata, Charles S. Weinert, and Lawrence R. Sita* “Deconvoluting Steric and Electronic Substituent Effects on the Properties of Linear Oligostannanes: Synthesis and Characterization of a New Series Incorporating the -tBu2Sn- Group.” Organometallics 1998, 17, 2241-2248.
 
3.Charles S. Weinert, Charlotte L. Stern, and Duward F. Shriver* “Synthesis, Characterization, and Substitution Chemistry of [Bu4N]2[W6Cl8(OSO­2CF3)6].  A Versatile Precursor for Axially Substituted Clusters Containing the {W6Cl8}4+ Core.” Inorg. Chem. 2000, 39, 240-246.
 
4.Nicholas Prokopuk, Charles S. Weinert, Vance O. Kennedy, David P. Siska, Hee-Joo Jeon, Charlotte L. Stern, and Duward F. Shriver* “Synthesis and Structure of the Useful Starting Material [Bu4N]3[Nb6Cl12(OSO2CF3)6].” Inorg. Chim. Acta  2000, 300-302, 951-957.
 
5.Nicholas Prokopuk, Charles S. Weinert, David P. Siska, Charlotte L. Stern, and Duward F. Shriver* “Hydrogen-Bonded Hexamolybdenum Clusters: Formation of Inorganic-Organic Networks.” Angew. Chem., Int. Ed. Engl. 2000, 39, 3312-3315.
 
6.Charles S. Weinert, Charlotte L. Stern, and Duward F. Shriver* “Preparation of [Bu4N]2[W6Cl8F6] and Characterization of the Clusters [Bu4N]2[W6Cl8X6] (X = F, Cl, Br, I, NCO, NCS, NCSe, or OSO2CF3) by 183WNMR Spectroscopy.” Inorg. Chim. Acta 2000, 307, 139-143
 
7.Charles S. Weinert, Nicholas Prokopuk, Stephanie M. Arendt, Charlotte L. Stern, and Duward F. Shriver* “Preparation and Substitution Chemistry of [Bu4N]2[W6Cl8­(p-OSO2C6H4CH3)6].  A Useful Precursor for Pseudohalide, Acetate, and Organometallic Complexes Containing the {W6Cl8}4+ Core.” Inorg. Chem. 2001, 40, 5162-5168.
 
Publications from Postdoctoral Research (Purdue University):
8.Charles S. Weinert*, Phillip E. Fanwick, and Ian P. Rothwell* “Isolation and Chemistry of Tantalum(V) Compounds Containing Two Resolved 3,3’-Disubstituted-1,1’-bi-2,2’-naphthoxide Ligands.” Organometallics 2002, 31, 484-490.
 
9.Charles S. Weinert*, Phillip E. Fanwick, and Ian P. Rothwell* “Novel Germanium(II) Binaphthoxide Complexes: Synthesis and Crystal Structure of (R, R)-[Ge{OC20H10-(OSiMe3)-2’-(SiMe3)2-3,3’}2] and (R)-[Ge{O2C20H10(SiMe2Ph)2-3,3’}{NH3}]; Catalytic Function of Ge[N(SiMe3)2]2 for the Mono-Silylation of 3,3-Disubstituted-1,1’-bi-2,2’-naphthols.” J. Chem. Soc., Dalton Trans. 2002, 2948-2950.
 
10.Charles S. Weinert*, Phillip E. Fanwick, and Ian P. Rothwell* “A Germanium-Silver Complex Containing a Ge-Ag Bond, Ag[Ge(OC6HPh4-2,3,5,6)3(AgOSO2CF3)]·4 C6H6.”  Acta Cryst. 2002, E58, m718-m720.
 
11.Charles S. Weinert*, Andrew E. Fenwick, Phillip E. Fanwick, and Ian P. Rothwell* “Synthesis, Structures, and Reactivity of Novel Germanium(II) Aryloxide and Arylsulfide Complexes.” J. Chem. Soc., Dalton Trans. 2003, 532-539.
 
12.Charles S. Weinert*, Phillip E. Fanwick, and Ian P. Rothwell* “Synthesis and Structures of the Group 1 Metal /Germanium Cage Complexes [M(μ2-OC6H3Ph2-2,6)3Ge] (M = Li, Na, K, Rb, Cs); Periodic Trends and Alkali Metal Dependent Arene Bonding.” J. Chem. Soc., Dalton Trans. 2003, 1795-1802.
 
13.Charles S. Weinert*, Phillip E. Fanwick, and Ian P. Rothwell* “Synthesis of Group 1 Metal 2,6-Diphenylphenoxide Complexes [M(OC6H3Ph2-2,6)] (M = Li, Na, K, Rb, Cs) and Structures of the Solvent-Free Complexes [Rb(OC6H3Ph2-2,6)]x and [Cs(OC6H3Ph2-2,6)]x: One )2Dimensional Extended Arrays of Metal Aryloxides.” Inorg. Chem. 2003, 42, 6089-6094.
 
14. ] Jennifer L. Walding, Phillip E. Fanwick, and Charles S. Weinert* “Syntheses and Reactivity of the Bulky Germanium(IV) Trisamide Compounds BrGe[N(SiMe3)2]3 and LiGe[N(SiMe3)2]3.  X-Ray Crystal Structures of BrGe[N(SiMe3)2]3 and [(Me3Si)2N]3Ge(CH2CH2CH2CH3).”  Inorg. Chim. Acta 2005, 358, 1186-1192.
 
15.Charles S. Weinert*, Phillip E. Fanwick, and Ian P. Rothwell. “Synthesis of the Tantalum-Hydride Complex (R,R)-[Ta(O2C20H10{SiMe3}2-3,3’)2(H)] and Reactivity with Aldehydes, Ketones, Acetylenes, and Related Substrates: A Reagent for the Asymmetric Hydrogenation of Prochiral Carbonyl Species.”  Organometallics 2005, 24, 5759-5766.
 
Publications from Independent Scientific Career (Oklahoma State University):
16.Esla Subashi, Arnold L. Rheingold, and Charles S. Weinert*.  “Preparation of Oligogermanes via the Hydrogermolysis Reaction.”  Organometallics 2006, 25, 3211-3219.
 
17.Charles S. Weinert.  “Germanium Organometallics.”  In Comprehensive Organometallic Chemistry III; Crabtree, R. H., Mingos, D. M. P., Eds.; Elsevier: London, 2007; Vol. 3, Chapter 13, pp. 699-808. INVITED REVIEW.
 
18. Anthony E. Wetherby, Jr., Stacy D. Benson, and Charles S. Weinert*.  “Reaction of Bis(bis(trimethylsilyl)amido)mercury(II) with 3,3’-Disubstituted Binaphthols: Cyclization via an Intramolecular Electrophilic Aromatic Substitution Reaction.”  Inorg. Chim. Acta 2007, 360, 1977-1986.
 
19.Anthony E. Wetherby, Jr., Lindy R. Goeller, Antonio G.  DiPasquale, Arnold L. Rheingold, and Charles S. Weinert*.  “Synthesis and Structures of an Unusual Germanium(II) Calix[4]arene Complex and the First Germanium(II) Calix[8]arene Complex and their Reactivity with Diiron Nonacarbonyl.”  Inorg Chem. 2007, 46, 7579-7586.
20.    Charles S. Weinert. "An NMR (1H and 77Se) NMR Investigation of the Reaction of
Ge[N(SiMe3)2]2 with Mesitylselenol: Formation of (MesSe)4Ge."  Main Group Met. Chem. 2008, 30, 93-100.
21.    Anthony E. Wetherby, Jr., Lindy R. Goeller, Antonio G.  DiPasquale, Arnold L. Rheingold, and Charles S. Weinert*. "Metal-Dependent Reactions of Bulky Metal(II) Amides Ge[N(SiMe3)2]2 with 3,3'-Disubstituted Binaphthols (HO)2C20H10{SiR3}2-3,3’: Selective Conversion of One Equivalent -OH Group to a Silyl Ether -OSiMe3."  Inorg Chem., 2008, 47, 2162-2170.
22.    Monika L. Amadoruge, Antonio G.  DiPasquale, Arnold L. Rheingold, and Charles S. Weinert*. "Hydrogermolysis Reactions Involving the a-Germylated Nitriles R3GeCH2CN (R = Ph, Pri, But) and Germanium Amides R3GeNMe2 (R = Pri, But) with Ph3GeH: Substituent Dependent Reactivity and Crystal Structures of Pri3GeGePh3 and But3Ge[NHC(CH3)CHCN]."  J. Organomet. Chem., 2008, 693, 1771-1778.
23.    Anthony E. Wetherby, Jr., Arnold L. Rheingold, Christa L. Feasley, and Charles S. Weinert*. "Synthesis and Crystal Structure of a Germanium(II) Calix[6]arene Containing Unusual Diamidosilyl Ether Groups."  Polyhedron, 2008, 27, 1841-1847.
24.    Monika L. Amadoruge, James A. Golen, Arnold L. Rheingold, and Charles S. Weinert*. "Synthesis, Structure, and Reactivity of Discrete Branched Oligogermanes."  Organometallics, 2008, 27, 1979-1984.  Cited in Chemical and Engineering News May 5, 2008.
25.    Monika L. Amadoruge, James R. Gardinier*, and Charles S. Weinert*. "Substituent Effects in Linear Organogermanium Catenates."  Organometallics, 2008, 27, 3753-3760.
26.    Monika L. Amadoruge and Charles S. Weinert*, "Singly Bonded Catenated Germanes: Eighty Years of Progress."  Chem. Rev., 2008, 108, 4253-4294.  INVITED REVIEW.
27. Charles S. Weinert. “Syntheses, Structures, and Properties of Linear and Branched
Oligogermanes.”Dalton Trans. 2009, 1691-1699.INVITED PERSPECTIVE
REVIEW.
28. Rebecca A. Green, Arnold L. Rheingold, and Charles S. Weinert*.“Synthesis of
the Germanium(II) Calixarene {p-But8calix[8]arene}Ge4 and its Reaction with Fe2(CO9:
Generation of the Germanium(II)/Iron(0) Complex {p-But8calix[8]arene}Ge4[Fe(CO)4
2.”Inorg. Chim. Acta 2009, 362, 3159-3164.

29. Monika L. Amadoruge, Claude H. Yoder, Julia Hope Conneywerdy, Katie Heroux,

Arnold L. Rheingold, and Charles S. Weinert*.“73Ge NMR Spectral Investigations of

Singly Bonded Oligogermanes.”Organometallics 2009, 28, 3067-3073.

30.Rebecca A. Green, Curtis Moore, Arnold L. Rheingold, and Charles S. Weinert*.

“Formation and Structures of Germanium(II) Aryloxo/Oxo Clusters.”Inorg. Chem.

2009, Articles ASAP, DOI: 10.1021/ic900915q.