Using Catalysts To Make Catalysts: Titanium-Catalyzed Hydroamination To Access P,N-Ligands for Assembling Catalysts in One Pot

Abstract

Using a diamido-bis­(amidate) titanium precatalyst, the hydroamination of alkynylphosphines afforded phosphinoenamine products. After reduction, 2-aminophosphines are prepared in excellent yield and on gram scale. A broad variety of alkynylphosphines and primary amines with different electronic and steric features are tolerated in this sequential transformation, enabling the rapid assembly of a collection of ligands. Additionally, intermediate phosphinoenamines can be used directly as proligands for coordination to transition metals using protonolysis or salt metathesis reactions. These transformations result in easy-to-use one pot protocols to prepare metal P,N-complexes for catalysis or small molecule activation.

Synthesis of Ti Complexes Supported by an ortho-Terphenoxide Ligand and Their Applications in Alkyne Hydroamination Catalysis

“…Quite interestingly, there is only a single report of a Ti-catalyzed hydroamination with this aniline (hydroamination of ethynyldiphenylphosphane). 33 Exploring this exceptional case further, an attempted hydroamination of phenylpropyne with p-CF 3 −C 6 H 4 NH 2 using 10% Ti(NMe 2 ) 4 also resulted in no reaction (Figure S69), indicating that there may be an underlying compatibility issue of this aniline with Ti catalysts.…”

“…1 H NMR analysis of the reaction mixture reveals likely decomposition of the precatalyst, as the chemical shifts of the ligand have changed without obvious formation of the Ti imido species (Figure S58). Quite interestingly, there is only a single report of a Ti-catalyzed hydroamination with this aniline (hydroamination of ethynyldiphenylphosphane) . Exploring this exceptional case further, an attempted hydroamination of phenylpropyne with p -CF 3 –C 6 H 4 NH 2 using 10% Ti­(NMe 2 ) 4 also resulted in no reaction (Figure S69), indicating that there may be an underlying compatibility issue of this aniline with Ti catalysts.…”

Group IV Complexes with Sterically Congested N-Aryl-adamantylcarbamidate Ligands

“…The substituents R′ and R″ allow to influence of steric as well as electronic properties of the amidates. Very often, R″ is an aryl group such as phenyl, pentafluorophenyl, or ortho -substituted aryl groups , but alkyl substituents have also been used in this ligand. , The addition of the metal-bound dialkylamido group onto the CN double bond has not been observed, but occasionally, the dimethylamido ligands show a peculiar reactivity, leading to metallaaziridines via liberation of an amine . The amidate ligands commonly act as bidentate Lewis bases with very few exceptions leading to pentacoordinate group IV transition metal centers, ,, coordination numbers smaller than five have not been observed for this compound class up to now.…”

Titanium-Catalyzed Hydroamination of an Organometallic Acetylide to Access Copper Enamides

“…Meanwhile, the hydroamination of such starting materials is attractive, as it is an efficient method to prepare bifunctional molecules. For example, there have been examples of alkyne-substituted ethers, boranes, stannanes, and phosphines that can undergo catalytic hydroamination to make N,Br-, − N,N-, − N,B-, and N,P-substituted , alkenes (Scheme a). To date, there has been one reported example of catalytic, intramolecular N–H addition across a transition-metal-substituted acetylide, a hydroauration reaction, which features ring closure by C–N bond formation to give a Au indolide derivative (Scheme b). , Intermolecular variants of such reactions were unexplored before this work (Scheme c).…”

“…Our group has developed a commercially available diamido-bis­(amidate) Ti hydroamination precatalyst for anti-Markovnikov terminal alkyne hydroamination . This precatalyst can tolerate a broad variety of substrates, including α-heteroatom-substituted alkynes. ,− Mechanistic studies have shown that our Ti precatalyst first reacts with primary amine substrates to generate a Ti imido intermediate that undergoes a [2 + 2] C–N bond forming cycloaddition step (Scheme a). , We have found that polarized alkynes are the preferred substrates with this Ti precatalyst. Thus, we proposed that metal acetylides, with their highly polarized CC functionality, would be suitable substrates for our Ti hydroamination precatalyst (Scheme c).…”