Let's proceed **systematically** according to your requirements: using only **quantitative physicochemical data** extracted from the information above, and minimizing speculative generalization.

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## Step 1: **Compile Quantitative Physicochemical Data**

The following table summarizes values directly extracted **from the PubChem database** for the four ligands:

| **Ligand** | **MW (g/mol)** | **TPSA (Å²)** | **H-bond Donor** | **H-bond Acceptor** | **Rotatable Bonds** | **XLogP** |
|:---|:---:|:---:|:---:|:---:|:---:|:---:|
| **bis(1-adamantyl)-[3,6-dimethoxy-2-[2,4,6-tri(propan-2-yl)phenyl]phenyl]phosphane** | 640.9 | 18.5 | 0 | 2 | 9 | 11.8 |
| **dicyclohexyl-[2-[2,4,6-tri(propan-2-yl)phenyl]phenyl]phosphane** | 476.7 | 0 | 0 | 0 | 7 | 10.1 |
| **ditert-butyl-[2-[2,4,6-tri(propan-2-yl)phenyl]phenyl]phosphane** | 424.6 | 0 | 0 | 0 | 7 | 8.5 |
| **ditert-butyl-[3,6-dimethoxy-2-[2,4,6-tri(propan-2-yl)phenyl]phenyl]phosphane** | 484.7 | 18.5 | 0 | 2 | 9 | 8.4 |

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## Step 2: **Primary Criteria for Classification**

With no explicit [Specified_physicochemical_Properties] categories listed, I will use common, structurally and functionally relevant **quantitative properties**:

1. **Polarity (TPSA, H-bond acceptors)**
2. **Hydrophobicity (XLogP)**
3. **Molecular size (MW)**

### **Polarity - Topological Polar Surface Area (TPSA) and H-bond Acceptors**

- TPSA = 0 means non-polar (no polar functional groups).
- TPSA > 0 (here: 18.5) indicates some polar surface, but generally <20 Å² is quite low, still very hydrophobic.  
- H-bond acceptor count: 0 or 2, no donors in any ligands (all are anhydrous phosphines).

### **Hydrophobicity (XLogP)**

- All have **XLogP > 8**, indicating strong hydrophobic character.  
- Range: 8.4 to 11.8 (all very high, threshold for "very hydrophobic" is usually >3 or 4).

### **Size (MW):**

- MW spans from ~425 to ~641 g/mol; all are large; two cluster at the lower end (~425–485), two at the higher end (~477–641).

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## Step 3: **Classify Into Groups (MAX 3)**

Let's search for the most **quantitatively justified breakpoints:**

### **Option 1: Polarity (By TPSA and H-bond Acceptor Count)**
- **Group 1 (Minimum Polarity): TPSA = 0, H-bond acceptors = 0:**  
  - dicyclohexyl...phosphane  
  - ditert-butyl...phosphane  
- **Group 2 (Low, but Nonzero Polarity): TPSA = 18.5, H-bond acceptors = 2:**  
  - bis(1-adamantyl)-[3,6-dimethoxy...]phosphane  
  - ditert-butyl-[3,6-dimethoxy...]phosphane

### **Option 2: Hydrophobicity (XLogP)**
- All XLogP values are > 8  
- Potentially one group, but bis(1-adamantyl)...phosphane is meaningfully higher (11.8) than others (10.1, 8.5, 8.4).
- However, the span (8.4 to 11.8) is narrow in relative terms (all extremely hydrophobic).  
- No strong basis to divide strictly on XLogP alone.

### **Option 3: Size (MW)**
- bis(1-adamantyl)-...phosphane is outlier at 640.9
- Others: 476.7, 484.7, 424.6—could be a "large" versus "very large" split
- Difference is not functionally supported unless classes were tied to, e.g., solubility/cell permeability, which is not requested explicitly.

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## Step 4: **Final Classification**

Based **strictly on quantitative data** and following the instruction to form no more than three groups, **polarity (TPSA and H-bond acceptors)** provides the clearest, most justifiable split, especially given the methoxy-containing variants.

### **CLASSIFICATION**

#### **Group 1: Nonpolar Ligands**
- **TPSA = 0, H-bond acceptors = 0**
    - dicyclohexyl-[2-[2,4,6-tri(propan-2-yl)phenyl]phenyl]phosphane
    - ditert-butyl-[2-[2,4,6-tri(propan-2-yl)phenyl]phenyl]phosphane

#### **Group 2: Very Slightly Polar Ligands**
- **TPSA = 18.5, H-bond acceptors = 2** (due to 3,6-dimethoxy substituents)
    - bis(1-adamantyl)-[3,6-dimethoxy-2-[2,4,6-tri(propan-2-yl)phenyl]phenyl]phosphane
    - ditert-butyl-[3,6-dimethoxy-2-[2,4,6-tri(propan-2-yl)phenyl]phenyl]phosphane

### **Alternative:** If strictly grouping by hydrophobicity or MW, all could be placed in ONE ‘highly hydrophobic, large, and almost nonpolar’ class, but the above grouping by measurable polar surface area and acceptor count is more justified by quantitative data.

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## **Summary Table**

| **Class Name** | **Ligands** | **Key Quantitative Criteria** |
|---|---|---|
| **Group 1: Nonpolar** | dicyclohexyl-[2...]; ditert-butyl-[2...] | TPSA = 0; H-bond acceptor = 0 |
| **Group 2: Slightly Polar (Methoxy)** | bis(1-adamantyl)-[3,6-dimethoxy...]; ditert-butyl-[3,6-dimethoxy...] | TPSA=18.5; H-bond acceptor=2 |

**Ambiguities:** No substance straddles groups according to these quantitative cutoffs.

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### **If you wish for further subdivision by size, hydrophobicity, or rotatable bonds (not as clear), please specify desired property.**

**This classification is strictly based on TPSA and H-bond acceptor count, reflecting structural features measurable in a physical database, and corresponds to the presence of methoxy groups.**