Ancillary ligands modification

Discovery of biaryl monophosphine ancillary ligand modification... 

The NLO properties of organometallic and coordination complexes are also rich (21, 184, 279-296). Metal-alkyne complexes were first reported 1960 (297) and have recently attracted significant interest because of their potential in materials applications (2, 298). Studies of these types (299) have resulted in the development of structure-NLO response relationships for quadratic optical nonlinearities (p-value), which increase with valence electron count and ease of oxidation of metal. The amplitude is also tunable by ancillary ligand modification and substitution. Select small alkynyl complexes have been shown to exhibit p values at 1064 nm > 2600 x 10 ° esu (299). 

In the transformation of a 1-alkyne to a vinylidene in the coordination sphere of a transition metal, the migrating hydrogen atom plays a key role. Usually, ancillary ligands on the metal are only spectators and do contribute to small modifications of the bonding properties of the metal fragment. However, if a hydride is present as a ligand to the transition metal center, it may interfere with the alkyne to vinylidene transformation. This may open up new selective and efficient routes to vinylidene complexes. 

One critical drawback of the aforementioned direct arylations is the inability to predictably control the site-selectivity of these reactions. For example, the Pd-catalyzed arylation of naphthalene affords varying ratios of ocp arylated isomers depending on the aryl sonrce and the reaction conditions (Schemes 24.9,24.10, and 24.11). Catalyst-based control sctvcs as a powerfnl alternative to systematically modulate the site-selectivities of organometallic transformations. Modification of the steric and electronic nature of the ancillary ligands has the potential to allow the preferential functionalization of the desired C—H bond. However, catalyst-based control remains challenging for Pd-catalyzed C—H functionalizations since these transformations genraally employ simple Pd salts that do not contain readily tunable ligands. 

Among neutral water soluble phosphines, PTA (PTA = l,3,5-triaza-7-phosphat-ricyclo[3.3.1. IJdecane) has received increasing attention in past and recent literature due to its versatility in synthetic modifications, use as ligands and interesting properties as either free compound or as ancillary ligand to metals, with applications covering homogeneous catalysis, material science, luminescence and medicinal chemistry [1,2]. 

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